The diagnosis of [human] P. carinii infection is dependent upon morphologic identification of the organism, making the staining properties of P. carinii important to the cytologist engaged in clinical service or research. Several special stains specific for P. carinii are described, the staining characteristics of the organism in Papanicolaou and in hematoxylin and eosin stains are described. The successful identification of P. carinii with the latter 2 stains has not been reported previously. Because these stains are often used on lung preparations, it may be possible to identify P. carinii when using these latter 2 techniques; for optimal results, it is essential to utilize 1 or more of the special stains.