In short-term experiments rats received single doses of 50, 100, and 500 μmoles/kg of the cryptating agent A 222. A dose-related increase in the activities of GOT and GPT in the serum was observed 6 h after treatment, reaching values up to 11 and 3 times that of the controls, respectively. However, the enzyme activities returned to the control levels within 3 days. The activity of alkaline phosphatase and the levels of protein and cholesterol in serum were not altered during the observation period of 7 days. Histopathological examinations did not show any changes in the liver, kidney, heart, lung, thymus, spleen, or intestine. The elevations of GOT and GPT seem to be due to a transient liver lesion, since no histopathological alterations of the liver became apparent. These results show that after single applications of A 222 at all doses used, no severe lesions occur in the observed organs.