Seventeen wistar rats were injected with cortisone acetate twice a week subcuteneously. After 7 weeks

pneumocystis pneumonia of rats was induced successfully. The cysts of Pneumocyst carinii were identified by phase-contrast microscope

Giemsa’s stain

Gomori’s methenamine silver nitrate stain and Chalvardjian’s toluidine blue-O stain simultaneously. A characteristic parentheses-like structure was found by Gomori’s stain in cyst wall. This structure has important value for differential diagnosis of pneumocystis pneumonia. The pathological changes were thickening of alveolar wall and infiltration of lymphocytes and monocytes. A few of honeycomb-like infiltration were found in the alveolar cavity. The Ultrastructures of trophozoite

precyst and cyst were observed by transmission electron microscope