The general aims of this study were to assess the effects of exercise on the health for early postmenopausal women by searching for the minimum effective dose in a systematic literature review and by conducting two randomized, controlled exercise trials. Early postmenopausal women have not been a common study group for exercise training. It was not until the 1980s that any good quality, randomized controlled trials (RCT) were carried out on postmenopausal women. Three reports were published in the 1980s. In the first half of the 1990s seven research reports were published, and in the second half of the 1990s nine appeared. After 2000 until June 2004 seven RCT reports appeared in the literature. Thus the effects of exercise on health are only partly known for this age group of women. The RCTs on the effects of exercise on maximal aerobic power, body composition and muscular strength showed that early postmenopausal women are trainable. But very few or none of the studies used light intensity aerobic training, fractionated aerobic exercise or resistance training with simple equipment. Very few or none of the studies showed what would be the effective exercise dose to improve submaximal aerobic capacity, blood pressure, body composition, carbohydrate and lipid metabolism, flexibility, and postural control. Feasibility-related information was also very sparse in these RCTs. With these questions in mind, the design of the experimental part of this study was formulated. The effects of six light-to-moderate intensity, continuous, and fractionated walking and resistance training programs on the health-related fitness of sedentary early postmenopausal woman were assessed in a two RCTs. The possible interactions of hormone-replacement therapy (HRT) on the results was also studied. In addition the feasibility and safety of these exercise programs were assessed for the sedentary participants. The participants were healthy, sedentary women, 2 - 10 years past the onset of menopause and between the ages of 48 and 63 years. An equal number of women with and without HRT were accepted. In the two studies of this research project, Study I and Study II, 134 and 121 participants, respectively, were randomized, HRT users and non-users separately, into exercise and control groups. The exercise intensity was planned to range from light-to-moderate (i.e. 45%, 55% or 65% of the maximal aerobic power (VO2max)). The weekly exercise volume was set at 1500 kcal or 1000 kcal. The exercise frequency was chosen to be 5 days a week, and the length of intervention was 15 or 24 weeks. Each day's training was continuous or fractionated (in Study I) into two equal sessions with at least a 5-hour interval. There was also a short resistance training program in Study I. Among the six exercise regimens of this study, the minimum effective dose of exercise needed to improve most of the selected cardiorespiratory and morphological fitness components (maximal aerobic power (VO2max) as measured by a maximal exercise test, submaximal capacity as measured by heart rate levels corresponding to 65% and 75% of the VO2max, and the proportion of body fat estimated by skinfold measurement) was the smallest exercise dose. It included walking at an intensity of 45% VO2max on 5 days a week, expending 1000 kcal (46 minutes) in weekly exercise for 24 weeks. The minimum effective exercise dose to improve the metabolic components (blood glucose, diastolic blood pressure and body mass) and also the rest of the chosen cardiorespiratory and morphological fitness components of health-related fitness (HRF), was the largest exercise dose. It included walking at an intensity of 65% VO2max continuously or fractionated into two exercise bouts on 5 days a week, expending 1500 kcal in weekly exercise in one (47 minutes) or two (2 x 24 minutes) exercise bouts per training day for 15 weeks. Approximately 15-20 minutes of moderate resistance training twice a week was combined with walking. This exercise regimen also improved walking performance and lower-extremity strength. The participants using and not using HRT had equal results for all of the chosen variables of HRF. These exercise regimens were feasible for the participants. They adhered well to the program. The dropout rate was low. There was only a small risk of injury. Most of the participants did not consider the exercise program to be too strenuous. Approximately half of the participants in the continuous exercise groups had some mild, transient lower-extremity complaints, especially at the beginning of the exercise intervention. Those in the fractioned exercise groups had statistically significantly fewer lower-extremity complaints. Starting a regular exercise program seemed to provide the participants with more positive experiences than remaining sedentary in the control group did, regardless of the exercise dose. The largest exercise regimen used in this study seems to be a feasible, practical minimum dose for health-enhancing physical activity for sedentary, early postmenopausal women to use to start improving most of the components of HRF. For more definite improvements, and also for improving other components of metabolic, musculoskeletal and motor fitness (lipids, muscle performance of the trunk and upper extremities, balance and flexibility), the exercise dose should be increased. This study increased the knowledge on light intensity aerobic training for early postmenopausal women. It is the first study to show effects of fractionated aerobic exercise in this age group of women. It is also the first study to show any effect of exercise training on diastolic blood pressure and fasting blood sugar concentration in healthy, early postmenopausal women. It is also one of the few studies that used an exercise training program that can be performed home based; walking and resistance training with simple equipment. Feasibility-related information was also actively gathered. This is the first study to show that fractionated exercise causes fewer exercise-related lower limb problems that continuous. There still remain unanswered questions concerning the effects of exercise on health-related fitness on early postmenopausal women. More RCTs are needed, especially on the effects of exercise on lipid levels, balance and flexibility. The interactions of HRT and exercise should be studied more in randomized, controlled settings.