Cryptosporidia have been associated with neonatal diarrhea in calves and other animals, and are transmissible between species. A reliable method for detecting cryptosporidia is needed due to their prevalence in livestock. Giemsa staining shows cryptosporidia as unstained or faintly stained, but can be confused with yeast. A modified Ziehl-Neelsen stain was developed for better detection. The staining procedure involves: drying the smear, fixing in methanol, staining with carbol fuchsin, differentiating with sulfuric acid, counterstaining with malachite green, and mounting. Cryptosporidia appear as red, densely stained bodies against a green background, with some being lightly stained, possibly oocysts. The method allows detection at 200-400x magnification. The carbol fuchsin dye may vary, so steps 5 and 7 should be adjusted based on the dye. The Ziehl-Neelsen method is more reliable than Giemsa for distinguishing cryptosporidia from yeast. It is easier than flotation methods. This technique is suitable for fecal samples and intestinal mucosa scrapings, and helps in differential diagnosis. The method was developed by Henriksen and Pohlenz at the State Veterinary Serum Laboratory and Iowa State University. References include studies by Anderson, Angus, Heine, Moon, and Nagy. (Received September 29, 1981). Reprints can be requested from Henriksen.Cryptosporidia have been associated with neonatal diarrhea in calves and other animals, and are transmissible between species. A reliable method for detecting cryptosporidia is needed due to their prevalence in livestock. Giemsa staining shows cryptosporidia as unstained or faintly stained, but can be confused with yeast. A modified Ziehl-Neelsen stain was developed for better detection. The staining procedure involves: drying the smear, fixing in methanol, staining with carbol fuchsin, differentiating with sulfuric acid, counterstaining with malachite green, and mounting. Cryptosporidia appear as red, densely stained bodies against a green background, with some being lightly stained, possibly oocysts. The method allows detection at 200-400x magnification. The carbol fuchsin dye may vary, so steps 5 and 7 should be adjusted based on the dye. The Ziehl-Neelsen method is more reliable than Giemsa for distinguishing cryptosporidia from yeast. It is easier than flotation methods. This technique is suitable for fecal samples and intestinal mucosa scrapings, and helps in differential diagnosis. The method was developed by Henriksen and Pohlenz at the State Veterinary Serum Laboratory and Iowa State University. References include studies by Anderson, Angus, Heine, Moon, and Nagy. (Received September 29, 1981). Reprints can be requested from Henriksen.