The ability of RPMI 4788 cells, a human colon cancer cell line, to produce experimental metastases in the lung, intraperitoneal cavity, and liver was studied in nude mice. Injection of 2 X 10(6) tumor cells into the tail vein of nude mice produced metastatic lung tumors, and an intraportal injection of 5 X 10(6) cells produced metastatic liver tumors. An intraabdominal carcinomatosis with ascites was formed after an i.p. injection of 5 X 10(6) tumor cells. The nude mice with lung metastasis or intraabdominal carcinomatosis always died within a few weeks. Macroscopic observation showed that the number of lung metastatic nodules on day 21 after tumor inoculation was 311.3 +/- 78.2 (mean +/- SD) in BALB/C nude mice, and 187.5 +/- 26.7 in ICR nude mice. In survival experiments, the mice with intraabdominal carcinomatosis showed a mean survival of 29.0 +/- 1.7 (mean +/- SD) days in BALB/C nude mice and 43.6 +/- 6.1 days in ICR nude mice. These novel experimental models of metastases in nude mice produced by injection of RPMI4788 cells had high reproducibility and may be useful not only for the study of the metastatic process but also for testing anticancer drugs.