It is fifty years since the publication of the report on the isolation, from coal tar, and identification of the potent chemical carcinogen benzo(a)pyrene, the culmination of over 10 years of research instigated and directed by E.L. Kennaway. The events leading to that discovery are of interest in themselves. Subsequent progress in unravelling the metabolic fate of polycyclic aromatic hydrocarbons has contributed to our understanding of the mechanism of chemical carcinogenesis.