An eighteen-foot-high model of a ' chromosome puff ' has just been unveiled in Chicago. Some chromosomes ' puff' when they undergo intense genetic activity, and this model is based on the latest research into the microscopic world of the gene. The model was filmed under construction and after completion, and Professor John Maynard Smith of the University of Sussex and Dr. John Curdon of the University of Oxford discuss the implications of the sort of genetic research which the model exemplifies. Also: Scientists and War - Sir Solly Zuckerman talks about his new book Scientists and War which outlines his views on the impact of science on affairs civil and military.