Blubber samples from 21 harbor seals (Phoca vitulina), found dead on Danish beaches during the morbilli virus epidemic in 1988, have been analyzed for toxic coplanar chlorinated biphenyl (CB) congeners. The 21 samples consist of seven samples from 1-2-year-old animals (both males and females) from each of three geographical separate locations: The Limfjord, the Kattegat, and the Wadden Sea. The level of the CBs, defined as the sum of all the measured CB congeners, were highest in the samples from the Wadden Sea and lowest in the Limfjord samples. The quotient between highest level and lowest level was 4. Toxic equivalency factors given by Safe (1990) was used for calculation of the contribution to dioxin-like toxicity from the coplanar CB congeners, and the result was compared to literature data on polychlorinated dibenzo-p-dioxins and -dibenzofurans in harbor seal. CB congeners CB-118, CB-156, CB-157, and CB-105 were major contributors to sigma TEQ in all samples. The patterns of polychlorinated biphenyl congeners in harbor seals from the three locations were compared by principal component analysis. The two first principal components could separate the samples in groups corresponding to each of the three geographical locations. The geographical and biological variations were estimated from the data. It was shown, that the geographical variation was the largest. Possible reasons behind the geographical variation in CB congener patterns are discussed.