The H-4-II E enzyme induction bioassay was used for testing both pure reference substances and extracts of wildlife samples. Polychlorinated naphthalenes were found to be as active as enzyme inducers as certain coplanar polychlorinated biphenyls (PCBs). Also a mixture of polybrominated diphenyl ethers (Bromkal 70-5DE) was shown to induce enzyme activity. In extracts of herring, containing polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), bioassay and chemically derived TCDD-equivalents (TEQs) were nearly identical. When extracts containing other types of dioxin-like compounds as well were tested, the bioassay TEQs for most of them agreed well with chemical TEQs calculated for PCDDs, PCDFs and non-ortho PCBs. However, for ringed seal and whitefish, TEQs obtained from the bioassay were higher than those from the chemical analysis. Our results indicate that this bioassay is an excellent complement to chemical residue analysis and a useful tool in understanding the complex interactions of halogenated hydrocarbons. For risk assessment, such results should, however, be used most carefully as they are measured in vitro.