Previous work with macrolides suggests that this class of agents may have activity against cryptosporidiosis parasite. The aims of this study are to: (1) evaluate the safety and efficacy of ascending doses of clarithomycin (2) compare the absorption and tolerability of the tablet and liquid forms of clarithromycin; and (3) evaluate the impact of malabsorption, as measured by d-xy-lose absorption, on the bioavailability and efficacy of clarithromycin for AIDS related cryptosporidial enteritis.