The theme of biology for the past 20 years has been the origin of biological constancy. The theme of the next 20 years will be the origin of biological diversity. This program explains why it is essential to understand the complicated mechanism of the normal cell before we can really understand what happens when cancerous cells run riot. The film focuses on the distinguished and internationally known work of Dr. James Till and Dr. B. McCullough of the Princess Margaret Hospital, and is written by them.