The conference on "Chemical Structure-Biological Activity: Quantitative Approaches" was held in Prague, Czechoslovakia, on June 27-29, 1973. It took place under the auspices of the J .E. PurkynC! Czechoslovak Medical SOciety, the Czechoslovak Chemi­ cal SOciety, and the International Society of Quantwn Biology (Organizing Commit­ tee: A. David, Chairman; M. Tichy, Secretary General; K. Bo~ek, J. Kopeck~·, R. Zahradnik). This volume contains the lectures and communications presented at the conference. There has been an ever increasing interest, especially during the last eight years, in the study of the quantitative relationships between the chemical structure of substan­ ces and their biological activity (QSAR - quantitative structure-activity relationships). One of the reasons for this increasing interest has been the desire to fmd ways of estimating the quantitative characteristics of a given biological activity as well as to shorten time and reduce the costs of research into optimally active compounds. In contrast to qualitative studies seeking the critical biologically active group, the QSAR approach involves the search for that property, or those properties, which determine the magnitude of the biological effect. Methods of physical chemistry and quantum chemistry appear to be suitable for estimating the quantitative characteristics of the biological activity of different compounds. Forecasting the specific activity of a certain substance by means of theoretical methods is still a matter of future devel­ opment. One of the basic ideas of QSAR studies is to work with a series of chemical compounds thereby enabling the collection and classification of experimental data.