An outbreak of histomonad infection of an apparent atypical nature was diagnosed in a flock of about 850 Bobwhite quail. Mortality was 95% over a 3-week period. The most prominent gross pathologic lesions were in the livers: disseminated white foci of necrosis, 1 to 2 mm in diameter, and subcapsular multifocal splenic necrosis was seen occasionally; lower intestinal lesions were infrequent. Histologic examination of liver and spleen sections revealed focal necrosis associated with variable numbers of protozoal organisms identified as a Histomonad spp. Identification of the protoza was ascertained by electron microscopy. Histmonads were isolated from affected quail livers and propagated in specific-pathogen-free chicken embryos. Lesions produced in embryos were evaluated. Isolates of the organism were used to reproduce the disease in young Bobwhite quail.