Cryptosporidial infection in humans results in parasite-specific IgG, IgM, and IgA antibody responses, but little is known of the cell-mediated immune responses to cryptosporidial antigens. In a convenience sample of 35 Haitian residents, there was a high level of cryptosporidial exposure (>90%) as determined by immunoblot reactivity of serum against cryptosporidial antigens. An attempt was made to determine if there was a relationship between antibody and T cell-mediated responses to recombinant Cp23 antigen and how this correlated with reactivity to crude sporozoite antigen preparations (SAg). T cell reactivity was greater against SAg (57%) than to Cp23 (34.3%) as measured by [³H]thymidine incorporation. Proliferative responses to Cp23 were significantly correlated with SAg responses. By enzyme-linked immunosorbent assay, most persons had IgG responses to both SAg (91.4%) and to recombinant Cp23 (88.5%). Antibody responses were greater among persons who exhibited T cell responses to SAg and Cp23. This study demonstrates that recombinant Cp23 antigen could be a useful antigen for detection of both antibody and cell-mediated responses in epidemiologic studies.