The work presented here deals with the status of glutathione-S-transferase (GST; E.C. 2.5.1.18), the major enzyme of the phase II detoxification pathway, in bovine filarial worms Setaria cervi. GST activity was determined in various subcellular fractions of bovine filarial worms S. cervi (Bubalus bubalis Linn.) and was found to be mainly associated with cytosolic and microsomal fractions. The respective specific activities of the enzyme from cytosolic and microsomal fractions of S. cervi females were determined to be 0.122 +/- 0.024 and 0.010 +/- 0.0052 micromol/min/mg protein, respectively. Cytosolic enzyme was found to possess optimal activity between pH 6.5 and 7.5, whereas the microsomal enzyme showed a broad pH optima, centered at pH 6.0. Kinetic studies on the cytosolic and microsomal forms of the enzyme revealed significant differences between them, thereby indicating that microsomal GST from S. cervi is quite distinct to the cytosolic protein catalyzing the same reaction.