In order to estimate the combined effects of UFT with other anticancer agents, a nude mouse experimental system (NMES), and a subrenal capsule assay (SRCA) were investigated. Three human tumor xenografts were serially transplanted into nude mice and examined. These were; EH-1 established from esophageal cancer, SH-6 from gastric cancer and CH-3 from colon cancer. The antiproliferative effects were estimated in accordance with the NCI therapeutic protocol. Significant antiproliferative effects were obtained only in NMES and a positive relationship was observed between the two assays (p less than 0.05). In the groups which were treated with a single agent, positive tumor responses were observed against mitomycin C in SH-6, against cis-DD platinum in SH-6 and EH-1, and against adriamycin in EH-1, respectively. On this study the synergistic, additive and subadditive effects were defined as the positive combined effects. The combination of MMC and UFT produced positive combined effects for all xenografts in both assays.