Milk samples of 14 women were analyzed for PCBs (polychlorinated biphenyls), p,p'-DDE, and HCB (hexachlorobenzene) during 11 intervals of a 120 day-lactation period. A general downward trend in residue levels was evident, and a statistically significant decline was observed for residue levels of PCBs (P less than 0.01) and HCB (P = 0.02) on the milk fat basis. Primipara (n = 9) had from 1.5 to 2.1 times higher mean residue levels than mothers nursing their second or third child (n = 9). Significant declines in residue levels during lactation of the first child were found, while no pronounced changes in residue levels were observed during lactation of the second or third child. Overall, residue levels in this study were lower than corresponding levels found earlier in Norway, and within the range of the corresponding levels found in another Norwegian human milk survey done at the same time.