The content of organohalogenated compounds in spent bleach liquor from different bleaching stages in a sulphate and a sulphite plant has been determined by a combination of glass capillary gas chromatography, gas-liquid chromatography/mass spectrometry and neutron activation analysis. Several compounds which have not been reported before have been identified including halogenated derivatives of dimethyl-propylnaphthalenes and alkylated catechols. The unconcentrated effluents, non-polar and total extracts were tested for mutagenic activity with Ames' Salmonella test. Spent bleach liquors from most bleaching stages as well as the total effluents contained mutagenic compounds. Addition of liver microsomes for metabolic activation reduced the mutagenic activity in all stages except for the first chlorination stage in the sulphate plant. Two isomers of chloro-, bromo-, and dichloro-p-cymene previously determined in effluents from bleaching plants were synthesized from the parent molecule. Both bromo- and dichloro-p-cymene exhibited weak mutagenic activity in the Salmonella test system. Liver microsomes reduced the effect slightly. The chlorinated cymenes were found to account for up to 18% of the total organically-bound chlorine in the non-polar extracts.