1. The urinary and biliary excretion of 14C-labelled m-cresol, 1-naphthol and o-chlorophenol were investigated in 12 species of freshwater fish (bitterling, Rhodeus sericeus amarus; bream, Abramis brama; crucian carp, Carassius carassius; goldfish, Carassius auratus; gudgeon, Gobio gobio; guppy, Poecilia reticulata; minnow, Phoximus phoximus; perch, Perca fluviatilis; roach, Rutilus rutilus; rudd, Scardinius erythropthalmus; three-spined stickleback, Gasterosteus aculeatus; tench, Tinca tinca) when immersed in sub-lethal concentrations of the compounds in the aquarium water for 48 h. 2. The sulphate and glucuronic acid conjugates of 1-naphthol and o-chlorophenol were detected in both the aquarium water and the bile of all the fish species. 3. The oxidation product of m-cresol, m-hydroxybenzoic acid, and the sulphate conjugate of the phenol, were excreted into the aquarium water of all species except the guppy, which did not excrete m-hydroxybenzoic acid. In addition to these two metabolites, the glucuronic acid conjugate of m-cresol was found in the bile of all species, except for guppies whose small size precluded study of biliary excretion.