Abstract
Studies of in vitro excystation of Cryptosporidum parvum from calves showed that sporozoite yields were optimum when oocysts were treated with sodium hypochlorite, then incubated at 37.degree.C for 60 min in the presence of taurocholic acid solutions at pH about 7.0. Trypsin was not required for excystation and high concentrations were inhibitory. Studies using protease inhibitors and direct assays for proteolysis failed to implicate proeolytic enzymes as effectors of excystation. The results suggest that Cryptosporidium uses excystation mechanisms that are different from those used by Eimeria spp.