In experiments to assess the changes in testis protein and enzyme activities induced by exposure to sodium fluoride (NaF) and sulfur dioxide (SO2), ninety-six adult male Wistar rats were divided randomly into four groups of twenty- four rats each. One group was left untreated as controls, and the other three groups were administered, respectively, for eight consecutive weeks, (1) 100 mg NaF/L (45 mg F–/L) in their drinking water, (2) SO2 in ambient air (15 ppm SO2, 4 hr/day), or (3) were exposed to both NaF and SO2 together. In comparison with the control group, the combination of NaF and SO2 resulted in lower protein levels and higher lactate dehydrogenase (LDH) activities in the testis of male rats than in the groups treated by NaF or SO2 alone. The activity of gamma-glutamyl transpeptidase (g-GT) decreased significantly in the NaF+SO2 group and in the SO2 group at week 4, and then increased markedly at weeks 6 and 8 in the same group. However, an increase in the activity of Na+K+- and Ca2+-ATPases in the SO2 group and the NaF+SO2 group occurred at week 2 and then decreased at weeks 4 and 6, respectively. Mg2+-ATPase activity at week 4 in the testis of male rats was significantly lower in all three treatment groups. These changes in protein and spermatogenesis-dependent enzymes undoubtedly affect the physiological functions of the testis, which may thereby cause low sperm motility.