Lead is a toxic metal and major environmental problem in many parts of the world. It is a cause of reproductive failure, infertility and teratological abnormalities. It is a known cause of neurological damage and learning difficulties in children, and lead-induced renal damage, cardiovascular and musculoskeletal toxicity are well documented. Lead is a mild mutagen but induces a number of epigenetic responses including inflammatory changes and immunological suppression, impairment of essential trace metal metabolism and ionic balances, sub-cellular changes of membranes, inhibition of enzymes in the cell cycle and mitochondrial damage, with chromosomal aberrations and clastogenicity. Lead is carcinogenic in certain strains of rodent and is shown to be a transplacental carcinogen in mice. Lead should be considered as a putative carcinogen in humans although many of the published studies claiming to show carcinogenicity of inorganic or organo-lead compounds make insufficient allowances for co-exposure to other environmental carcinogens or smoking. Lead is a contaminant of cigarette tobacco. On the basis of existing evidence, lead should be regarded as a potential cause of brain cancer and possibly cancers of the lungs, gastrointestinal tract and kidney. No epidemiological reports have been seen to implicate lead in transplacental carcinogenesis in humans and further research is required to establish whether it is a cause of Wilm’s renal tumour in children. Present views indicate that a contamination level of 10 μg l−1 is an achievable safe level for lead in drinking water.