The most interesting and portentous biological experiment of the 20th century authoritatively described by one of the three principal executants. --Sir Peter Medawar The education of the transforming principle, i.s., genes, as DNA ranks with the contributions of Darwin and Mendel. Here is the chronicle of that revolutionary advance in biology told in eloquently humble fashion by one of the insiders . . . . This work gives another glimpse into the daily joys and frustrations of the scientific life, a story rarely told with such directness and candor. --Joshua Lederberg, Ph.D., president, Rockefeller University Maclyn McCarty's The Transforming Principle is an elegantly written story of the discovery that DNA is hereditary material--perhaps the most important discovery in biology of the twentieth century. Also, it is the story of the scientists and the science which represents compelling reading for all science watchers. --Paul A. Marks, M.D., president, Memorial Sloan-Kettering Cancer Center