Sir Gus Nossal is distinguished for his work on cellular aspects of immunity. He was the first to demonstrate, in association with Lederberg, that isolated lymphoid cells (plasma cells) could liberate antibody and that, in doubly immunised animals, the great majority of cells produced one type of antibody only. He has made important contributions to the understanding of immunological tolerance, and his recent studies on the distribution of antigen in the lymph node have opened up an important new field. His reviews have played a major part in developing modern concepts of the genetic aspects of immunology.