Antigens were extracted from the epicuticle/cuticle of intact femaleOnchocerca volvulususing 2% 2-β-mercaptoethanol and 1% SDS. In Western blot analysis a human infection serum selected for its high antibody titre against whole worm homogenates did not recognize any component solubilized by 1% SDS. However, the same serum did bind at least 7 antigens among the material extracted with 2-β-mercaptoethanol. These antigens have apparent molecular weights (Mr) of: 15 000, 18 000, 28 000, 78 000, 98 000, 120 000 and 200 000. In ELISA using this preparation as target antigen, 151 out of 153 human infection sera gave positive results. AnOnchocerca-specific IgG1 monoclonal antibody, designated Cam1, recognized the 28 000Mrantigen, which is the most prominent antigen detected by Western blot analysis using human infection sera. In ELISA, using material affinity-purified with Cam1 as target antigen, 149 out of 153 human infection sera gave a positive IgG response. From a cDNA library three expressing clones were isolated with a rabbit serum raised against 2-β-mercaptoethanol solubilized material. One of these clones was recognized by the monoclonal antibody Cam1.