A phase II study of a new anthracycline, (2''R)-4'-0-tetrahydropyranyladriamycin (THP) was performed on 37 patients with gastrointestinal cancer in 6 co-operative study institutions. Twenty-five patients out of 37 were evaluable for response according to the Koyama-Saito's criteria. THP was administered weekly at doses of 10 to 30 mg/body or every 3 to 4 weeks at doses of 40 to 60 mg/body intravenously. Of the 14 patients with gastric cancer, we obtained one complete response and 3 partial responses (response rate 28.6%), and of the 6 patients with rectal cancer, we obtained one partial response (16.7%). Leukopenia of less than 3 X 10(3)/mm3 and erythrocytopenia of less than 300 X 10(4)/mm3 were seen in 48% and 26% of cases. Neither cardiotoxicity nor hair loss were seen. These results suggest that THP is useful in the treatment of patients with gastrointestinal cancer.