To analyse the efficacy of diethylcarbamazine (DEC), tetramisole and chlorpromazine on the longevity and activity of glucose-6-phosphatase and succinate dehydrogenase in the microfilariae recovered from the peripheral circulation of the rats before and after the treatment. Methods: Setaria cervi worms were implanted in white rats via laparotomy and microfilaraemic rats were divided into 4 groups. Groups 1, 2 and 3 were treated with DEC, tetramisole and chlorpromazine respectively, while Group 4 served as infected control. Longevity of microfilariae and differential leucocyte counts were recorded till the disappearance of microfilariae from peripheral blood. Glucose-6-phosphatase and succinate dehydrogenase enzymes were localized in the microfilariae recovered from normal and treated rats. Results: The microfilariae survived for 48 days in untreated rats while survival was reduced to 15, 21 and 27 days after treatment with DEC, tetramisole and chlorpromazine, respectively. Eosinophils and neutrophils increased during 2nd and 3rd weeks, whereas the lymphocytes increased during 4-7 weeks. DEC treatment resulted in slight decrease in the localization of succinate dehydrogenase but not in glucose-6-phosphatase. Tetramisole and chlorpromazine treatment did not show any appreciable change in the localization of both the above enzymes. Conclusions: DEC proved the most effective drug which cleared the microfilaraemia within 15 days and reduced the activity of succinate dehydrogenase to some extent followed by tetramisole and chlorpromazine which took more time for the clearance of microfilariae and had no effect on the localization of both glucose-6-phosphatase and succinate dehydrogenase.