Abstract: The present paper reports the use of colorimetric method to determine the blood level of F-30066 in portal vein and heart in rabbits. By spectrophotometry, paper and column chromatography, the metabolites of F-30066 in the intestine and urine of the host were investigated.The therapeutic effect of the drug as shown by different routes of administration, including the oral route, was compared. Owing to the absorption of F-30066 in the gastro-intestinal tract, a certain concen- tration of the drug was found in the portal blood, F-30066 could be decomposed in liver, a part of it being re-excreted into intestine after inactivation.The transformation pro- ducts did not show any effect on schistosomes in mice. After oral administration of F-30066, two metabolites were detected in urine. None of them showed any killing effect on schistosome. When the solution of F-30066 was exposed to diffused sunlight, the drug was de- composed and became inactive. When 15 mg/kg of F-30066 in suspension were given intravenously to rabbits three times daily for 14 days, no therapeutic effect was observed. When a dose of 45 mg/kg of this drug was administered intramuscularly once daily for 10 days, the result was disappointing.F-30066 was still found at the site of injec- tion four weeks later. Intraperitoneal injection of 4 mg/20 g of F-30066 to mice did produce a satisfactory response; its blood content determined 1/2, 1, and 2 hours after injection was found to be 8.2, 2.2, and 1.6 μg/ml respectively.Neither intravenous nor intramuscular injection could result in such a high level.It seemed likely that the therapeutic effect of F-30066 was closely related to the concentration in blood.