We evaluated the diagnostic performance of a Cryptosporidium immunoenzymatic assay (ELISA). Fecal samples were collected from 94 HIV-seropositive patients. All specimens were processed with a commercially-available ELISA to detect C. parvum specific coproantigen and with a modified Ziehl-Neelsen stain (ZNm) microscope exam. Overall, sensitivity of the immunoenzymatic test was 100%, with a specificity of 96%; positive and negative predictive values were 89% and 100%, respectively. The commercial ELISA and ZNm proved to be valuable diagnostic tools for Cryptosporidium infection.