66 BALb/c mice

38 Wistar rats

10 guinea-pigs and 6 rabbits were injected by hydrocortisone acetate subcutaneously twice a week

respectively. Their feces were examined for Cryptosporidium oocysts by auramine-phenol stain

modified fast-acid stain and safranin-methylene stain simultaneously.The Cryptosporidium oocyst positive rate in the immunosuppressive mice was 71.21%(47/66)

but in the immunosuppressive rats the positive rate was 34.21%(13/ 38) only. The Cryptosporidium oocysts in the mice were divided intc two types: the large type oocysts were 7.47μm X 5.90μm and the small type oocysts were 4.61μm X 4

33μm. The Cryptosporidium oocyst was not found in the feces from guinea pigs or rabbits. No oocysts were found in the feces from the mice injected subcutaneously or gaven orally by dexamethasone.This result suggested that the immunosuppressive mice injected by hydrocorti-sone acetate subcutaneously may be a useful animal model for studying Cryptospo-ridiosis