Starch microspheres 40 micrometers in diameter, which are rapidly degraded by serum amylase, have been administered through hepatic arterial catheters to five patients with primary and metastatic liver cancer to determine whether (1) arterial blood flow through the liver could be temporarily blocked, and (2) such occlusion at the level of the arteriolar capillary bed would enhance regional uptake and catabolism and decrease systemic exposure to simultaneously administered hepatic arterial bischlorethylnitrosourea (BCNU). It was possible with 10 ml of microspheres (9 X 10(6) microspheres/ml) injected into the hepatic artery to transiently (for 15-30 minutes) reduce hepatic flow by 80-100% in the five patients. When BCNU (50 mg/m2 in one minute) was given with microspheres there was a 30-90% reduction in systemic nitrosourea exposure and in peak levels. No myelosuppression was noted and hepatic toxicity consisted of acute pain due to BCNU and 1.5-2.0 fold transient enzyme elevations. One patient with cholangiocarcinoma showed a partial response lasting three months; three patients had stable disease and one patient with colon carcinoma had progressive disease. Thus, this pilot study suggests that concurrent intra-arterial microspheres and BCNU may have the potential to improve selective regional drug effect with marked diminution in systemic toxicity.