The efficacy and safety of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment administered separately or in combination for Wuchereria bancrofti infections were assessed in 1996-98 in a randomized double-blind placebo-controlled field trial in Ghana: 1425 individuals from 4 lymphatic filariasis-endemic villages, 340 of whom were microfilaria (mf)-positive before treatment, were randomized into 4 groups to receive albendazole alone, ivermectin alone, combination of albendazole and ivermectin, or placebo, respectively. Individuals were followed for 5 days after treatment to record any adverse reactions, and the effect of treatment on microfilaraemia was monitored in night-blood samples after 3, 6 and 12 months. Treatment efficacy was analysed for 236 mf-positive individuals who had > or = 100 mf/mL of blood and who were also present for examination at 12 months after treatment. Compared to the placebo group, the ivermectin and combination groups both showed statistically significant reductions in geometric mean mf intensities at the follow-up examinations (to 6.7% and 0.9%, 9.9% and 6.9%, and 21.7% and 11.4% of pre-treatment levels, respectively, at 3, 6 and 12 months after treatment). Compared to the ivermectin group, however, the reduction in the combination group was significantly greater only at 3 months after treatment, but not after 6 or 12 months. The albendazole group showed a slow but non-significant reduction over the same period. Adverse reactions were few and mostly mild (no severe reactions were recorded), and no significant differences were observed between the treatment groups. Both ivermectin and combination treatment thus appeared effective and safe for treatment of lymphatic filariasis, but the difference in efficacy was minor and the study did not provide clear evidence for the combination drug therapy, as compared to ivermectin therapy alone, to be superior for control of lymphatic filariasis.