The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment alone and in combination on Wuchereria bancrofti microfilaraemia, antigenaemia and clinical manifestations was compared 12 months after treatment in a double-blind placebo-controlled field trial carried out in Ghana in 1996-98, to evaluate the potential of these treatments for control. Both ivermectin and combination treatments resulted in pronounced reductions in microfilaraemia among individuals who were microfilaria positive before treatment. Among individuals who were positive for circulating filarial antigen before treatment, antigen levels increased considerably over the 1-year period after treatment in the placebo group, whereas they decreased in the ivermectin and combination groups. However, the post-treatment difference reached statistical significance in neither microfilaraemia nor antigenaemia between the ivermectin and the combination groups. Albendazole treatment alone showed only a minor effect on microfilaraemia and antigenaemia. No effect of the treatments on the incidence of new cases of microfilaraemia or antigenaemia, or on clinical manifestations, was observed. Both ivermectin and combination treatment thus appeared effective for control of W. bancrofti infections, but the difference in efficacy between the 2 treatments after 12 months appeared to be minimal.