Pharmacological actions of 5-fluorouracil (Fu), an antipyrimidine agent, were investigated. In mice, LD50 were the doses of 730 ( sc), 1, 010 ( ip) and 41. 6 ( ic) mg/kg respectively. Chroni c convulsion, lateral turning or rotation of the whole body were observed in application of Fu in the brain of mice and its CD50 was the dose of 18. 15 mg/kg. For subacute toxicity, the rates of death w ere 50% during 30-40 days in the group of 20 mg/kg and 10∼50% during 50∼60 days in the group of 5∼10 mg/kg/day respectively. At that time decrease of testis weight and increase of spleen weight were noticed. The movement of the excised frog heart was accelerated at the dose of 0. 2 mg/ml of Fu, and inhibited at 2 mgiml. The mov e ment of the excised rabbit intestine was accelerated at the dose of 1 mcg/ml of Fu and inhibited at 0. 5 mg/ml. it has no effec t on the excised auricular vessels of the rabbit and dose of 1 mg/m1 of Fu increased the permeability of rabbit skin vessels. Temporary fall of blood pressu r e and decrease of respiration were observed at the dose of 10 mg/kg of Fu in the urethane-anesthetised rabbit. Bradycardia (lengthens of PQ inter val) took place at the dose of 4 mg/kg of Fu and tachycardia (shortens of ST interval) at the dose of 20 mg/kg. Local irritation of Fu was not observed. Fu, therefore, has not remarkab l e pharmacological actions at the therapeutic doses.
