Hexachlorocyclohexane (HCH) has been banned for use in technologically advanced countries; however, it is still in use in tropical countries like India. Earlier we reported the degradation of HCH isomers by Sphingomonas paucimobilis within 12 days of incubation. Here we report the role of different factors that could enhance the degradation rate of HCH isomers. We found that an increase in the cell number from 10(2) to 10(8) cells/ml resulted in an increased degradation rate of HCH isomers viz, alpha, beta, gamma, and delta -HCH. While alpha -HCH and gamma -HCH disappeared completely from the medium within 3 days of incubation, a maximum of only 90% and 85% degradation was observed for beta and delta -HCH, respectively. We have also observed that adapted cultures degraded HCH isomers more efficiently than did the normal cultures.