Human milk samples from 28 mothers at Oslo City Hospital, Norway, were collected in 1991 and analyzed for individual polychlorinated biphenyl (PCB) congeners, IUPAC numbers 28, 74, 99, 101, 105, 114, 118, 128, 138, 141, 153, 156, 157, 170, 180, 194, and 206, plus selected non-ortho-substituted compounds, IUPAC numbers 77, 126, and 169. Sum DDTs (sum of concentrations of DDT and related compounds), hexachlorobenzene (HCB), oxychlordane, transnonachlor, and sum hexachlorocyclohexanes (HCHs) (sum of concentrations of alpha-HCH, beta-HCH, and gamma-HCH) were also determined. The mean levels of sum DDTs, HCB, oxychlordane, transnonachlor, and sum HCHs were 338, 41, 9, 19, and 36 ng/g, respectively, in human milk fat. p,p'-DDE and beta-HCH accounted for 81 and 93% of sum DDTs and sum HCHs, respectively. The mean level of sum PCBs (sum of mean concentrations of 20 individual congeners) was 372 ng/g milk fat. A very good correlation was found between sum PCBs and PCB-153 (r = .97). Sum PCBs determined on a capillary column was found to account for 62-79% of total PCBs calculated by using the packed column method used in previous human milk surveys in Norway. Comparison with previous results revealed that the mean sum PCB, HCB and sum DDT levels were decreased by 70, 65, and 75%, respectively during the past 9 yr. The contribution of individual PCDD/PCDF (earlier Norwegian study) and non- and mono-ortho-substituted PCB congeners to the total calculated toxic equivalent values was assessed, and the PCBs were found to constitute a major part of the TCDD equivalents in human milk, with PCB-126 as the main contributor.