Twenty men with moderate infection of Onchocerca volvulus were studied in a double-masked, controlled clinical trial to compare the safety and efficacy of oral diethylcarbamazine (DEC) with topical DEC lotion. Visual acuity and colour vision did not alter during the 6 months of observation, although 2 patients receiving DEC lotion and 3 patients receiving oral DEC developed either visual field constriction or optic atrophy. Fluffy corneal opacities were common in both groups. Intraocular microfilariae also appeared in both groups but to a greater extent in those receiving DEC lotion. New chorioretinal changes developed in 4 men receiving lotion and in only 1 receiving tablets. It is concluded that DEC lotion offers no advantage over tablets in the treatment of ocular onchocerciasis and in fact may be associated with more ocular complications than the conventional oral treatment.