The percent of conventionally stained circulating neutrophils containing abnormal giant granules in Chediak-Higashi mink, cattle and mice is highly variable and strikingly less than the 100% found in neutrophils from similarly affected humans. In contrast, using either peroxidase or Sudan Black, it can be demonstrated that 100% of circulating neutrophils in all affected individuals of the four species studied contain the abnormal granules. Minor species differences in the shape of the granules were noted. The significance of these findings as well as the variations in granular staining by the several techniques employed are discussed.