In this volume are collected 30 papers, 9 round table discus­ sions and 11 communications presented at the ASI Course on "The use of human cells for the evaluation of risk from physical and chemical agents", sponsored by NATO and organized by ENEA. The aim of the Course was to present different scientific ap­ proaches and technical advices in order to get dose-effect relation­ ships which are the basis for risk evaluation. The scientific back­ ground which is behind this approach was extensively discussed. Emphasis has been given to the use of human cells or human data in order to attempt to have a correct and realistic evaluation of the damage in humans. There are many criticisms on the use of animal data for human risk evaluation because of differences between species and between strains within the same species: differences in metabolism, activa­ tion processes and DNA repair ability makes uncertain the extrapola­ tion of animal data to humans. Also data obtained using specific strains or highly inbred strains in order to reduce the variance are not applicable due to the heterogeneity of the human population connected with individual responses. In this respect only the use of human cells enable us to detect the individual variability and to identify sensitive subpopu­ lations that would be at greater risk. My appreciation to Pieranita and Alberto Castellani for the as­ sistance during the meeting and to Giuseppe Biondi for his help in some of the editorial work.