An aerobic bacterium, isolated from a contaminated site, was able to degrade sulfanilic acid (4-aminobenzenesulfonic acid) and was identified as Pseudomonas paucimobilis. The isolate could grow on sulfanilic acid (SA) as its sole carbon and nitrogen source and metabolized the target compound to biomass. The bioconversion capacity depended on the sulfanilic acid concentration; greater than 98% elimination of the hazardous compound was achieved at low (10 mM) sulfanilic acid concentration, and the yield was greater than 70% at 50 mM concentration of the contaminant. The maximum conversion rate was 1.5 mmol sulfanilic acid/h per mg wet cells at 30 degrees C. Ca-alginate-phytagel proved a good matrix for immobilization of P. paucimobilis, with essentially unaltered biodegradation activity. Removal of sulfanilic acid from contaminated industrial waste water was demonstrated. SDS-PAGE analysis of the crude extract revealed novel proteins appearing upon induction with sulfanilic acid and related compounds, which indicated alternative degradation mechanisms involving various inducible enzymes.