This year marks the tenth anniversary of the International Symposium on Medical Virology. In the Foreword to the book of the 1980 Symposium, we stated, "However, the challenges still lying ahead are more numerous than our past accomplishments". Little did we know at the time, that within a few years the spread of human immunodeficiency virus type I was going to occur. This worldwide epidemic has, like no other disease in recent history, awakened the scientific community and the public at large. It is a reminder to all of us that regardless of our vast technical advances, Nature provides such great opportunity for biological diversity, that it will always be one step ahead of our scientific knowledge. Although our understanding of virology, molecular biology and immunology have increased by leaps and bounds over the last decade, we are still at the point of being unable to effectively control the spread of this viral infection. We hope that our Symposium this year has helped researchers to come together and exchange' ideas, so that our growing knowledge of viral infections will help produce better approaches to control them. Luis M. de la Maza Irvine, California Ellena M. Peterson March, 1991 v ACKNO~EDGEMENTS It would be impossible to single out all those individuals who helped us make this Symposium a reality, however, we would like to take this oppor­ tunity to express our appreciation for their efforts.