The toxicity of Z-103 (catena-(S)-[mu-[N alpha-(3-aminopropionyl) histidinato(2-)-N1,N2,O:N tau]-zinc], CAS 107667-60-7) was evaluated in mice and rats after single administration. LD50 values in mice were 1269 mg/kg for males and 1331 mg/kg for females by the oral route, 220 mg/kg for males and 165 mg/kg for females by the intraperitoneal route, and 758 mg/kg for males and 874 mg/kg for females by the subcutaneous route. LD50 values in rats were 8441 mg/kg for males and 7375 mg/kg for females by the oral route, 405 mg/kg for males and 422 mg/kg for females by the intraperitoneal route and more than 5000 mg/kg for both sexes by the subcutaneous route. No sex differences were observed. A decrease in locomotor activity, ventral posture, crouching, hypothermia and respiratory depression were observed in both mice and rats as the main clinical signs. In addition to these changes, induration, swelling and crust formation were observed at the subcutaneous injection site.