Hexachlorocyclohexane (HCH) is a broad spectrum insecticide still used in some of the developing countries, though developed countries have banned or curtailed its use. Even in those countries where the use of t-HCH has been discontinued for a number of years, the problem of residues of all isomers of t-HCH remains because of its high persistence. These insecticides in the soil disturb the delicate equilibrium between microorganisms and their environment. Few reports on the degradation of t-HCH isomers in soil are present in literature, and very little information is available on the effect of these t-HCH isomers on soil microflora. In the present study, an attempt has been made to see the microbial diversity in the uncontaminated soils and the effect of application of t-HCH on the soil microflora. The soil was spiked with t-HCH and incubated, at regular time intervals the soil samples were analyzed for microbial diversity as well as t-HCH isomers residues. The results show that at higher concentrations of t-HCH, microbial populations were inhibited and the inhibited populations did not reappear even after prolonged incubation. Potential t-HCH degrading cultures were isolated and subjected to further acclimation in order to enhance their degradation capacity. The results are presented and discussed in this paper. (C) 2006 Elsevier B.V. All rights reserved.