Abstract: The Pneumocystis carinii (PC) were isolated through bronchial alveolar lavage from PC pneumonia rats prepared by induction with prednisolone, and it was treated and purified with anti - rat - common leukocyte antigen monocolonal antibody. The ingesting ability of macrophage for PC and the effect of glucocorticoid were studied in vitro. The results showed that the PC could be ingested and degraded by peritoneal macrophage (PM_φ) and alveolar macrophage (AM_φ). The difference of uptake of mature cyst forms (MCFs) of PC between PM_φ and AM_φ was not significant (P＞0.05). The ingesting ability of AM_φ for PC in dexamethasone pretreatment group was inhibited after 60 min of phagocytosis in comparison with non ” pretreatment group (the uptake of MCFs of PC:10.08 士0.3/100M_φ vs 12. 25土0. 28/100M_φ,P＜0.05). The results suggested that the induction of PC pneumoni-a in rats with the glucocorticoid may be related to the inhibition of macrophage ingestion a-bility, and that macrophage may play an important role in the protection of the pathogenesis of PC.