A Study to Evaluate the Use of Nitazoxanide to Treat Cryptosporidiosis

Inclusion Criteria Patients may be eligible for this study if they: * Are 3 to 65 years old (need consent of parent or guardian if under 18). * Have AIDS. * Have a CD4 count less than or equal to 200 cells/mm3. (Note: Patients with a CD4 count greater than 200 cells/mm3 but who have had cryptosporidiosis for at least 4 weeks may be eligible for this study.) * Test positive for the parasite Cryptosporidium and have severe diarrhea (at least 4 bowel movements per day) for at least 2 weeks. * Have received treatment for cryptosporidiosis but have become reinfected after treatment. * Agree to practice abstinence or use effective methods of birth control (such as a condom) before and during the study. Exclusion Criteria Patients will not be eligible for this study if they: * Are pregnant. * Are infected with certain other parasites. * Have a history of certain intestinal diseases. * Have received certain medications.