In order to investigate the pathway of microbial degradation of synthetic soap, e. g., alkylbenzene sulfonate (ABS), the isolation of the ABS-decomposing bacteria was carried out. The most active strain among 8 strains of pseudomonas-like bacteria isolated utilized ABS for its growth in sulfate-free glucose-mineral medium. The optimum concentration of ABS for the growth was around 100ppm, and no growth was recognized in the absence of glucose.The decomposing activity of the bacterium was much accelerated by using p-hydroxybenzene sulfonate in the seed-culture. When cysteine was added, the rate of ABS-decomposition was considerably depressed as long as it was not completely consumed in the medium.The mechanism of cnzymatic decomposition of ABS is now under investigation, by using resting cells and cell-free enzyme preparations.