A six-age class dosage schedule of Diethylcarbamazine (DEC) of 50mg (1-2 years), 100mg (3-4 years), 150mg (5-8 years), 200mg (9-11 years), 250mg (12-14 years) and 300mg for above 14 years is being adopted for annual single dose MDA for LF elimination treat Wuchereria bancrofti microfilaria carriers. In order to increase the community compliance as well as to make the distribution easier during MDA, a revised 3 age class dosage schedule of 100mg (2-4 years), 200mg (5-14 years) and 300mg for above 14 years was evaluated for its tolerability and efficacy. By this change, it was observed that the 4-8 years age class is receiving 50 mg higher and 11-14 years age class is receiving 50mg lesser dose compared to the earlier class schedule. Therefore, the safety aspect in the age class of 4-8 years and efficacy component in the age class of 11-14 years were assessed. Apparently "healthy" asymptomatic microfilaraemic volunteers between the age class of 4-8 and 11-14 years were recruited for the study. The incidence of side reaction in the 4-8 years age class was 50.0% with 150mg dose and 66.7% with 200mg (P>0.05). No life threatening adverse reactions was observed in any dosage schedule. Fever, headache and myalgia, the predominant adverse reactions were mild and similar in both schedules. The mean intensity of the three major specific adverse reactions (fever, headache and myalgia) also did not differ significantly (P>0.05). For the purpose of LF elimination, efficacy in terms of reduction in mean microfilaria load is important. In the 11-14 year age class considerable reduction in the geometric mean density (GMD) was observed by day 90 and 180 post-therapy in both groups (250mg group and 200mg group) compared to pre-therapy level. By day 360 post-therapy, the difference was statistically not significant (P>0.05) (reduction of 72.2% in 250mg and 69.6% reduction in 200mg). The reductions in GMD were statistically significant when compared to pre-therapy levels in both the old (250mg) and new (200mg) doses. Thus, three- age class dosage schedule is as safe and efficacious as the six- age class schedule.