Carbon-limited aerobic batch enrichment cultures were grown and 17 bacteria able to degrade orthanilic acid (2-aminobenzenesulphonic acid), sulphanilic acid, sulphonamide, 4-sulphobenzoic acid, and benzene-, toluene- and phenolsulphonic acids were isolated. The organisms could each use one to three of the substances. Strain O-1, a sp., which utilized three of these compounds, was studied in detail. A complete mass balance was obtained for the growth of the organism in medium containing, for example, orthanilic acid, and a specific growth rate of 0·1 h was observed. Cell extracts desulphonated six aromatic sulphonates. The enzyme(s) was soluble and was not synthesized in succinate-grown cells. Enzyme activity [about 40 μkat (kg protein)] was dependent on the presence of catalytic amounts of NAD(P)H.