1 The concentrations of some organochlorine pesticides and polychlorobiphenyls have been determined in 193 samples of human milk collected between July 1989 and July 1991. 2 Comparison of the results with those from previous studies in 1979-80, and earlier, shows a continuing decline in residue levels except for polychlorobiphenyls. 3 The concentrations of organochlorine pesticides and polychlorobiphenyls in human milk samples from resi dents in the United Kingdom compare favourably with data obtained in other countries.