To examine the role of specific cytokines in mediating the clinical manifestations of human onchocercal disease, microfilariae-positive Ghanaian subjects with inflammatory ocular disease were compared with microfilariae- positive subjects without ocular disease. Onchocerca volvulus antigen (OvAg)- stimulated peripheral blood mononuclear cells (PBMC) from subjects with disease produced significantly more interleukin (IL)-10 (with disease = 447.34 vs. without disease = 292.22 pg/mL; P < .01) and IL-5 (with disease = 33.36 vs. without disease = 27.26 pg/mL; P = .02). OvAg-stimulated IL-4 and interferon (IFN)-γ levels were essentially undetectable in either group. When cytokine mRNA levels were measured by reverse transcriptase-polymerase chain reaction ELISA, persons with disease produced significantly more OvAg- stimulated IL-4, IL-5, and IL-10 mRNA (P = .03, <.01, .05, respectively). No difference in IFN-γ mRNA production by either group was seen. Addition of neutralizing αIL-10 antibody to OvAg-stimulated PBMC increased IFN-γ production to detectable levels in 20 of 24 persons.