A Gram-negative bacterium, Pseudomonas sp. strain SR3, was isolated from soil at a former wood treatment plant in north central Florida. The ability of this bacterium to degrade pentachlorophenol (PCP) was confirmed by growing cells in a basal salts medium in which PCP was the only source of carbon and energy. Degradation from a measured concentration of PCP was observed within 120 h of incubation in the presence of PCP-induced cells of Pseudomonas sp. strain SR3. Microtox 5 min EC50 toxicity tests revealed that aqueous solutions of PCP, measured concentrations 39-40 microgram/ml were toxic but that final biodegraded samples, 0.0006 microgram PCP/ml were nontoxic. However, bioassays with embryonic inland silversides, Menidia beryllina, showed that the biodegraded samples were embryotoxic or teratogenic. Results indicate that while biodegradation of PCP was nearly complete, intermediate metabolites of the degradation process or undergraded impurities in PCP were toxic or teratogenic.