Pneumocystis carinli is an established cause of pulmonary infections in immuno-compromised hosts. Several cytoiogical stains, such as Papanicolaou, Gomori methenamine sliver(GMS) and Diff-Quik have been used for detection of the organism, but occasionally can be laborious and, due to a degree of nonspecificity, may be misleading. We evaluated the diagnostic utility of immunocytochenmical stains that recognize P. carinii in bornchoalveolar lavage from experimentally Induced P. carinii pneumonia rats(n=15). In audition to routine stains for diagnosis by morphologic recognition of P. carinii on Papanicolaou, GMS and Diff-Quik stains, bronchoalveolar lavage samples were reacted with immunocytochemical stains using monoclonal antibodies(MAB) 092 and 902. In bronchoalveolar lavage P. carinii organisms were detected In 9 of 10 cases(90%) using each MAB 092 and 902, whereas GMS and Diff-Quik stains demonstrated P. carinii in 13(86%) and 11(73%) of 15 cases respectively. In lung tissue specimens(n=15) P. carinii organisms were well identified on GMS stain and immunohistochemical stains using MAB 092 and 902 in ail cases. We believe that the immunocytochemical staining using MAB 092 and/or 902 is a very useful and diagnostic tool In addition to GMS and Diff-Qulk stain to detect P. carinii organisms in bronchoalveolar lavage.