The effect of continuous and discontinuous locoregional chemotherapy with Floxuridine (FUdR) was studied in a standardized and controlled animal model, using the transplantable Novikoff hepatoma in Sprague-Dawley rats. The liver was perfused after transplantation with a total of 420 mg/kg FUdR, via a fully implanted osmotic minipump or miniport and catheter in the hepatic artery, either continuously (n = 22) from day 5 to day 12, or discontinuously (n = 28) on days 5 and 8. Viable tumor volume and peritumorous cell infiltration were measured. No reduction in tumor volume was attained using discontinuous therapy, in contrast to a highly significant reduction using continuous therapy (P less than 0.001). Significantly less cell infiltration was found after discontinuous than after continuous therapy. In conclusion, continuous locoregional chemotherapy with FUdR was the superior administration method on measurable tumor effect, when compared to discontinuous infusion.