The frequency, intensity and clinical features of onchocerciasis in the two ethnic groups (Blacks and Chachilla--an indigenous tribe) in the endemic foci of the disease in Esmeraldas province (Ecuador) were evaluated. The incidence of infection and intensity of the disease seen in both groups were directly related to the frequency of man-vector contact and not to racial factors. Both groups showed the same rate of positivity in both the hyperendemic and hypoendemic areas. Males of both groups had a consistently higher positivity rate than did females. The Chachilla were found to have a higher mean microfilarial density than Blacks in both types of endemic areas. Certain clinical features of the disease analogous to those seen in the African form were present only in Blacks. No lymphatic involvement or hypertrophic scarring was seen in the Chachilla, suggesting that in the Blacks there may be a generaically related predisposition to lymphatic complications of microfilarial infections.