Twenty-four transpositional mutants of aniline-assimilating Pseudomonas sp. AW-2 produced catechol from aniline and accumulated it in a cultural medium. Among the 24 mutants, strain B-9 produced a maximal amount of catechol (0.97 mg/ml) from 1 mg/ml of aniline in a 13.5-h growing culture containing pyruvate and casamino acids. The conversion rate of aniline to catechol was 82% on a molar basis. The catechol production by the resting cells increased in the presence of glycerol and citrate, and a maximal amount of catechol produced from 1 mg/ml of aniline reached 1.1 mg/ml at the conversion rate of 93% after 2 h of incubation. Enzymes catalyzing the synthesis of catechol from aniline were induced by aniline in strain B-9 cells.