Amygdalin has been used for a long time as an anticancer agent. But because of its toxicity, it is difficult to administer continuously for treatment of cancer. This paper was attempted to reduce the side effect and toxicity of amygdalin. That is, effects of cysteine and streptomycin on the toxicity of amygdalin were investigated in rats orally administered amygdalin. 1. The group administered only amygdalin 400 mg/kg was effected on the lung and body weight, hematocrit, hemoglobin, clotting time, SGOT and albumin value. That is, lung and body weight, hematocrit hemoglobin and albumin value were significantly decreased. SGOT and clotting time were significantly increased compared with those of normal group. 2. Weight of lung was significantly increased in the C group (administred amygdalin 400 mg/kg and cysteine 300 mg/kg), D group (amygdalin 400 mg/kg and streptomycin 10 mg/kg), E group (amygdalin 400 mg/kg, streptomycin 10 mg/kg and cysteine 200 mg/kg)and F group (amygdalin 400 mg/kg, streptomycin 10 mg/kg and cysteine 300 mg/kg). 3. Values of hematocrit and hemoglobin were significantly increased, and clotting time was significantly decreased, in the I group and F group compared with those of A group. 4. SGOT was significantly decreased in the C group, E group and F group compared with that of A group. 5. The blood cyanide concentration was significantly decreased in the E group and F group compared with that fo A group. 6. In short, coadministration of cysteine and streptomycin are considered to reduce the toxicity of amygdalin in rats orally administered.