This volume encompasses the Proceedings of the First International Colloquium on Physical and Chemical Information Transfer and Regulation of Reproduction and Ageing (Colloquium '74-PCITRRA), held at the F. Joliot­ Curie International House of Scientists, Varna, Bulgaria, October 7-14. This international event was made possible by the financial support afforded by the International Union of Biochemistry through Doctor P.N. Campbell, the International Union of Pure and Applied Biophysics through Doctor R.D. Keynes, UNESCO, and the Bulgarian Academy of Sciences. The characteristic and stimulating feature of the Colloquium'74-PCITRRA was the interdisciplinary audience (physicists, biologists, physicians, chemists, mathema­ ticians, engineers) and the orientation to information transfer and biological recognition in ageing. The at­ tention was focused on receptor transformation, espe­ cially that in ageing. Of special interest were the mathematical models and the theoretical basis of bio-information transfer, the age changes of the receptor recognition, the chemi­ cal information transfer in development, the hormone­ hormone interaction envisaged in their biophysical and biochemical aspects. The Colloquium '74 provided a very frank, critical and stimulating atmosphere for work and discussion on the latest results and concepts in topics of interest. The active role of the chairmen, Doctors. H.R. Arnstein, H.-J. Bartels, M. Blecher, J.A. Edwardson, M.R.P. Hall, E.V. Jensen, B.B. Saxena, J.R. Tata, and Ya.M. Varshavsky, was a great contribution in this respect and we would like to express our gratitude to them.