A phase II trial of gemcitabine (difluorodeoxycytidine) was conducted in 14 patients with advanced colorectal adenocarcinoma. Gemcitabine was administered intravenously over 30 minutes at weekly intervals for 3 consecutive weeks each month. The starting dose was 800 mg/m2, with dose escalation as tolerated. No complete or partial response were observed. Ten patients experienced progressive disease while on therapy. Toxic effects were primarily hematologic in nature. Grade 3 toxicities included leukopenia (one patient at 1000 mg/m2), granulocytopenia (two patients at 800 mg/m2), anemia (two patients at 800 mg/m2), and myalgia (one patient at 800 mg/m2). No grade 4 toxic effects or treatment-associated deaths were observed. Gemcitabine, at the doses and schedule used in this study, did not demonstrate activity against advanced colorectal adenocarcinoma.