The concentrations of selected organochlorine contaminants in Swedish human milk have been determined in a number of studies conducted at the National Food Administration during the 1980s. It was shown that the time of sampling post-partum (subsequent to childbirth) had little effect on the levels of the DDT complex, beta-HCH, HCB and PCBs in breast milk fat. However, the levels of these compounds decreased with increasing parity (number of children born). For this reason it is recommended that primiparae (women nursing their first child) be sampled when comparing levels over time and in milk from mothers from different geographical areas. The levels of organochlorine compounds in the fat of breast milk from primiparae living in different parts of Sweden were similar. Finally, a study on time trends in concentrations of these compounds in milk from mothers living in Uppsala showed that a marked decline in levels has taken place during the 1980s.