Levels of non-ortho-polychlorinated biphenyls (PCB), some mono-ortho-PCB, and resolved peaks of tetrato heptachloronaphthalenes are reported in biological and sediment samples from the Swedish environment. The results show that levels of individual PCB congeners, and especially PCB 126, may pose a greater threat to the environment than the 2,3,7,8-chlorinated dioxins and furans when expressed as 2,3,7,8-tetrachlorodibenzodioxin (TCDD) toxic equivalents. Polychlorinated naphthalenes are as widespread pollutants as PCB, and at some locations the pollution situation indicates a specific source, leading to a bioaccumulating hexachloronaphthalene contributing considerably to the total TCDD-like toxicity. A time trend study of guillemot eggs from the Baltic Proper seems to indicate that levels of non-ortho-PCB and -PCN have decreased since the 1970s.