A study of 40 Hereford cattle dwarfs in New Zealand confirmed that dwarfism in this country was morphologically the same as that described in North American Herefords and that its mode of inheritance was as an autosomal recessive trait. The histological architecture of growth plates was essentially normal but palisading columns were shorter and more irregular than in controls. A small proportion of cbondrocytes in dwarf cartilage showed increased areas of cytoplasmic metachromasia, which probably coincided with increased cystic dilations of endoplasmic reticulum containing granular material as noted by electronmicroscopy. The above growth-plate abnormalities were neither prominent nor consistent enough to be of diagnostic significance; nor do they currently help understanding of the underlying pathogenic mechanism of dwarfing. Histological and mucopolysaccharide excretion studies unequivocally demonstrated that this disease is not a mucopolysaccharidosis as had previously been reported.