Aims: To determine optimal environmental conditions for achieving biodegradation of alpha- and beta-endosulfan in soil slurries following inoculation with an endosulfan degrading strain of Pseudomonas aeruginosa. Methods and results: Parameters that were investigated included soil texture, soil slurry: water ratios, initial inoculum size, pH, incubation temperature, aeration, and the use of exogenous sources of organic and amino acids. The results showed that endosulfan degradation was most effectively achieved at an initial inoculum size of 600 mu l (OD = 0.86), incubation temperature of 30 degrees C, in aerated slurries at pH 8, in loam soil. Under these conditions, the bacterium removed more than 85% of spiked alpha- and beta-endosulfan (100 mg l(-1)) after 16 days. Abiotic degradation in noninoculated control medium within same incubation period was about 16%. Biodegradation of endosulfan varied in different textured soils, being more rapid in course textured soil than in fine textured soil. Increasing the soil contents in the slurry above 15% resulted in less biodegradation of endosulfan. Exogenous application of organic acids (citric acid and acetic acid) and amino acids (L-methionine and L-cystein) had stimulatory and inhibitory effects, respectively, on biodegradation of endosulfan. Conclusions: The results of this study demonstrated that biodegradation of endosulfan by Ps. aeruginosa in soil sediments enhanced significantly under optimized environmental conditions. Significance and Impact of the Study: Endosulfan is a commonly used pesticide that can contaminate soil, wetlands and groundwater. Our study demonstrates that bioaugmentation of contaminated soils with an endosulfan degrading bacterium under optimized conditions provides an effective bioremediation strategy.