To characterize the clinical and laboratory features of onchocerciasis in visitors to endemic areas and to compare them with those seen in endemic subjects, 20 returned visitors and 21 endemic subjects with onchocerciasis were evaluated. Dermatitis was the most frequent clinical finding among the returned visitors. None had nodules or eye disease and, in contrast to the endemic subjects, microfiladermia was often absent or of low density. All persons studied had antibody responses measurable by ELISA to both soluble Onchocerca volvulus antigen and a panel of diagnostic recombinant antigens. Eosinophil and IgE levels were significantly higher in the endemic group, as was the capacity of peripheral blood mononuclear cells from this group to produce the T helper cell-like cytokines interleukin-4 and -5. It is likely that the chronicity and intensity of infection in endemic subjects account for the clinical and immunologic differences observed between the 2 groups.