Abstract: Weconducted a clinical trial comparing LDCF (20 mg/m²/day x 5 days) to HDCF (200 mg/m:/day x 5 days) combined with 5-Fu (1000 mg/day x 5 days) by continuous intravenous infusionfor 120 hours in the treatment of advanced gastric and colorectal carcinoma. Fifty-two evaluablepatients entered into this trial. In the series of 31 patients with advanced gsstric carcinoma (1graded CR, 13 PR). the resPOnse rates for LDCF and HDCF patients were 50% and 41 %, respectively (p0. 05). Of 20 patiems with colorectal cancer (3 attained a PR) the re8POnse rates forLDCF and HDCF patiensts were 18 % and 11 % respectively (p0. 05). HDCF/5-Fu regimen wasnot superior to LDCF/5-Fu regimen. Main toxicities included stomatitis, phlebitis, diarrhea, skinrash, and mild myelosuppression. Stomatitis occured in HDCF group much higher (64. 9%) thanin LDCF group (24% ), Basing upon considerations of therapeutic effectiveness, tokicity, and const, the authors conclude from this trioal that optimal leucovorin dose is 20 mg/mm².