 C. parvum is a significant opportunistic infection in much of the developing world, where children may not have access to highly active antiretroviral therapy. There is currently no established therapy for chronic cryptosporidiosis in HIV infected children. The FDA has approved NTZ for the treatment of cryptosporidiosis diarrhea; however, there are no data on the safety and effectiveness of NTZ in HIV infected children. The purpose of this study is to evaluate the safety of different doses of NTZ in HIV infected children with chronic diarrhea caused by C. parvum. 