The origin of infection of a Colombian with ocular onchocerciasis was investigated; as a result, a seemingly small focus of onchocerciasis was discovered in the Pacific coastal region of western Colombia, the first to be found in that country. Onchocerca infections were found in 44 of 292 persons who lived along the Rio Micay or one of its tributaries. Most of the infected persons lived within a few kilometers of a small settlement known as San Antonio. Onchocercal nodules were found on only 10 persons, mostly on the thorax and hips. No more than two nodules were found on any person. Microfilariae were also found in relatively low numbers in skin snips in the positive cases. There were no severe ocular or dermal conditions attributable to the filarial infections.