Pseudomonas marginalis, capable of utilizing acetonitrile as the sole source of carbon and nitrogen, was isolated from an industrial waste site. P. marginalis metabolized acetonitrile into ammonia and acetate. The minimal inhibitory concentration values of different nitriles and amides for P. marginalis were in the range 5-300 mM. The bacterium was able to transform high-molecular-mass nitrile compounds and their respective amides into ammonia. The data from substrate-dependent kinetics showed that the K-m and V-max values of P. marginalis for acetonitrile were 33 mM and 67 nmol oxygen consumed min(-1) (ml cell suspension)(-1) respectively. The study with [C-14]acetonitrile indicated that nearly 66% of the carbon was released as (CO2)-C-14 and 12% was associated with the biomass. The enzyme system involved in the hydrolysis of acetonitrile was shown to be intracellular and inducible. The specific activities of the enzymes nitrile aminohydrolase and amidase were determined in the cell-free extracts of P. marginalis. Both the enzymes could hydrolyze a wide range of nitriles and amides. The present study suggests that the biodegradation of organic nitriles and the bioproduction of organic acids may be achieved with the cells of P. marginalis.