Male infertility is a significant health problem for which few aetiological factors have been identified. The role of occupational exposure is largely unknown but certain substances such as 1,2-dibromo-3-chloropropane, oestrogen, heat, lead and microwaves have been reported to impair spermatogenesis in workers. Other agents which interfere with reproductive performance in experimental animals such as cadmium, manganese, organophosphates and some solvents have not been studied sufficiently for their occupational risks to be fully known. Some occupational exposures, extensively studied, appear to convey little or no risk to male fertility including radiological exposure, anaesthetic gases and Agent Orange. It is clear that the range of substances potentially hazardous to male reproduction is great but the number of agents for which the evidence is unequivocal is very small.