In a phase II study, 32 patients with advanced pancreatic carcinoma were treated with intravenous 6-thioguanine. A 30-min infusion of 55 mg/m2 (starting dose) was administered once a day for 5 consecutive days, the course being repeated every 5 weeks. A median of two courses (range, 1-10) was administered. Among the 32 patients, 30 having measurable cancer and optimum follow-up were fully assessable for response. One patient achieved a partial response of extensive liver metastases (12+ months), and another patient had a transient minor response (5 weeks). Cancer in 27 of 30 assessable patients progressed during intravenous 6-thioguanine treatment. Myelosuppression, although frequent, was mild to moderate at these doses and did not result in significant morbidity. Nonhematologic toxicities were also mild. Our data suggest that intravenous 6-thioguanine given at this schedule is ineffective in previously untreated patients with advanced carcinoma of the pancreas.