1. N- and O-sulphoconjugation of various substrates were studied with human liver cytosol and purified cytosolic sulphotransferase in the presence of 3-phosphoadenosine 5-phosphosulphate. 2. Human liver cytosol catalysed N-sulphoconjugation of alicyclic and aryl-amines, and O-sulphoconjugation of hydroxysteroid and phenol. Activities of amine sulphoconjugation in the cytosol correlated well with those of hydroxysteroid but not with phenol. 3. Alicyclic amine sulphotransferase in human liver cytosol was purified to homogeneity by anion exchange, affinity and hydroxyapatite chromatography. Sulphoconjugating activities of alicyclic amine co-purified with those for hydroxysteroid conjugation. Subunit molecular weight of the purified sulphotransferase was 34 kDa. Contents of the purified enzyme correlated with the sulphoconjugating activities of hydroxysteroid and alicyclic amine. From these results, we concluded that the alicyclic amine sulphotransferase purified in this study was identical to hydroxysteroid sulphotransferse in human liver cytosol. 4. The results of this study indicate that hydroxysteroid sulphotransferase in human liver cytosol catalyses N-sulphoconjugation of alicyclic and aryl-amines. Hydroxysteroid sulphotransferase in the cytosol is reported to catalyse O-sulphoconjugations of various compounds including hydroxysteroids, bile acids, cholesterol, and aliphatic and benzylic alcohols. The present and previously reported results indicate that hydroxysteroid sulphotransferase in the cytosol catalyses both N- and O-sulphoconjugations of several substrates.