Cryptosporidium parvum, an intracellular protozoan parasite, is a frequent cause of chronic diarrhea in HIV-infected patients, causing significant morbidity and mortality. Highly effective antiparasitic treatment for this infection is not currently available. Paromomycin and azithromycin have some efficacy and have been used in combination in a small number of patients. Immune reconstitution with highly active antiretroviral therapy appears to be the most effective therapy, but this is not possible for all patients. Interferon gamma expression is strongly associated with control of cryptosporidiosis, and IL-12 is the cytokine primarily responsible for stimulation of interferon gamma expression in vivo. It is hoped that treatment with recombinant human IL-12 can result in stimulation of an intestinal cytokine response in AIDS patients with cryptosporidiosis and that response combined with chemotherapy can lead to the elimination of detectable numbers of Cryptosporidium oocysts from the stools.