Recent studies have indicated that sex hormones may regulate expression of murine glutathione S-transferase (GST) isozymes. Therefore, we have purified and compared GST isozymes of murine ovary and testis, two tissues with markedly different hormonal milieu. Isoelectric profiles of the GST isozymes of both these tissues were found to be closely similar. Both expressed one alpha-class GST (pI9.8), one pi-class GST (pI8.9), and three mu-class GSTs (pI8.5, 7.9, and 6.7). In addition, an isozyme (pI5.8) corresponding to the rat GST 8-8 was also expressed in both these tissues. Total GST protein/g tissue was about 1.7-fold more abundant in testis. The specific activities of the cationic isozymes of testis were 1.2- to 2.4-fold higher as compared to those of ovaries. On the other hand, the specific activities of the anionic testicular isozymes were 6.4- to 10-fold higher compared to the corresponding ovarian isozymes. Structural properties including the N-terminal sequences of the testicular isozymes were indistinguishable from those of their ovarian counterparts. The N-terminal sequence of the pi-class GST of both tissues was similar to that of mouse liver GST pi. The three mu-class GSTs of testis and ovary arise from the dimeric combinations of two subunits whose N-terminal sequences determined up to 24 residues were similar to those of mouse liver GST subunits mu 1 and mu 2. Although testicular and ovarian isozymes were structurally similar, Kcat values of some of the testicular isozymes were up to 10-fold higher than those of the corresponding ovarian isozymes. The substrate specificities were also significantly different for the corresponding isozymes of testis and ovary.