We performed combination chemotherapy adapted to chronotherapy with 5-fluorouracil, leucovorin, mitomycin C and cisplatin in 11 patients with gastric cancer and 7 with colorectal cancer. Treatment consisted of a 5-day course of continuous arterial or intravenous infusion of 5-FU (500 mg/body/day), arterial or intravenous infusion of leucovorin (20 mg/body/day) at 6:00 p.m. on days 1-5, arterial or intravenous infusion of mitomycin C (2 mg/body) at 9:00 a. m. on day 5, and arterial or intravenous infusion of cisplatin (20-80 mg/body) at 6:00 p.m. on day 5. The effective rate against gastric cancer was 73%; however, the effective rate against colorectal cancer was 29%. During and after this therapy, there was only a little appetite loss, nausea and stomatitis.