Two microorganisms able to grow in mineral salt medium containing styrene (0.1-1.0%) as the sole carbon source were isolated under static culture conditions. The two strains, LF-1 and KO-8-1, belong to Pseudomonas mendocina. Both strains utilize not only styrene but also toluene and heptanol as carbon sources. Cell viability and total cell count of both strains were higher when they were grown in the presence of 0.1% styrene than in the presence of 1.0% styrene. In the presence of 0.1% styrene, cell viability reached 2.3 x 10(8) cells/ml for strain LF-1 and 7 x 10(8) cells/ml in strain KO-8-1, and decreased gradually thereafter, Substrate utilization tests revealed that the substrate specificities of the strains differ, Styrene oxide was found as a degradation product in the culture.