Abstract: Pseudolycorine is an alkaloid isolated from Narcissus tazetta var. chinensis Roem, N. papyraceus or Lycoris radiata Herb. Both the free alkaloid and its hydrochloride showed marked inhibition on the growth of W-256 carcinosarcoma in rats under tolerable doses, but the inhibition on the growth of hepatoma, subcutaneous transplants of Ehrlich ascites cascinoma and S-180 in mice was not significant. The LD₅₀ of pseudolycorine injected intraperitoneally to rats was found to be 110(92.4～131)mg/kg. Intraveneous infusion of the drug caused slow lowering of the blood pressure in the cat, but the dose of the drug required to kill the cat is rather high (av. 881mg/kg). The subacute toxicity tests in the dogs showed that pseudolycorine may induce nausea, vomiting and anorexia, but it did not inhibit the bone marrow significantly. Some increase of the nonprotein nitrogen value in the dogs after adminstration of the drug was observed, but this might be caused by prerenal factors. Autopsy of the dogs showed no significant pathological changes in the viscera, including the heart, liver, spleen, lung, kidney and intestine. Phase I clinical trial of the drug is now in progress.