SummaryThe osteolathyrogenic action of β-mercaptoethylamine (cysteamine), when fed to rats as the hydrochloride, was confirmed. Cystamine was found to have similar properties. Gross and microscopic skeletal changes were similar to those produced by osteolathyrogenic nitriles. Aortic lesions were much less severe than when β-aminopropionitrile is fed, but medial swelling and lysis of elastic fibers were observed. These substances showed a narrow range of osteolathyrogenic activity, a dietary level of 0.2% cystamine ‡ 2HCl causing only very slight spinal curvatures, while a level of 0.5% was rapidly lethal to most animals.