Although suppressive therapy for onchocerciasis with intermittent ivermectin prevents the development of pathology in endemic populations, the clinical and immunologic effects of therapy in the absence of continued exposure are unknown. To address this question, 14 patients treated with ivermectin for onchocerciasis acquired >10 years ago during temporary residence in Africa were reevaluated. None had evidence of continued infection or pathology at follow-up. Although eosinophilia, serum IgE, and antifilarial antibody levels decreased after ivermectin therapy, none of these parameters was useful in predicting the resolution of symptoms in infected patients. Peripheral blood mononuclear cells isolated from patients at follow-up were more responsive to parasite antigen in vitro, which is as assessed by proliferation and production of interferon-gamma and interleukin (IL)-5. In contrast, antigen-induced levels of IL-10 were significantly decreased at follow-up, consistent with diminished down-regulatory factors rather than a switch from type 2 to type 1 immune responses.