SummaryA surface enriched fraction was prepared from adults ofOnchocerca volvulusby brief extraction of entire worms with detergent. This was then gel filtered to yield a low molecular weight fraction which functioned specifically in ELISA analysis. An identical result was also obtained when the related cattle parasite,O. gibsoni, was similarly fractionated and tested. The low molecular weight fraction contained at least four antigenic components when examined by coprecipitation and immunoblotting studies. One ml of packed worms yielded sufficient low molecular weight antigen to examine about 2000 human sera by the ELISA procedure, and the test was sensitive at human serum dilutions down to 1/400. A preliminary study with individual sera from Onchocerciasis endemic and non‐endemic areas of Southern Mexico yielded 0/24 false positives, 3/24 false negatives and a significant ELISA value in 21/24 sera from proven cases of Onchocerciasi