The effect of cyclosporin (CyA), FK 506, and mycophenolate mofetil (MPM) on tumor growth was investigated using syngeneic mouse colon carcinoma 38. Mice were laparotomized and the tumor cells were injected into the portal vein to establish liver metastasis. The animals were grouped as follows: groups A-1, B-1, and C-1 were given CyA [15 mg/kg body weight (BW)], FK 506 (0.15 mg/kg BW), and MPM (100 mg/kg BW), respectively, 30 min before tumor inoculation and daily for 5 days by gavage; groups A-2, B-2, and C-2 were given CyA (30 mg/kg BW), FK 506 (0.3 mg/kg BW), and MPM (200 mg/kg BW), respectively, with the same dose timing; and groups A-3, B-3, and C-3 received CyA (30 mg/kg BW), FK 506 (0.3 mg/kg BW), and MPM (200 mg/kg BW), respectively, on the 7th post-tumor inoculation day and on the following 5 days. The mean tumor diameter in groups A-1 and A-2 was greater than that in the control group and in groups C-1 and C-2 at 3 weeks (P < 0.05). The mean tumor numbers in groups A-1 and A-2 were greater than those in the control group and in groups C-1 and C-2 at 4 weeks (P < 0.05). With in vitro MTT assay, all three drugs acted cytostatically on tumor cells with a higher concentration (10(-6)-10(-4) mol/l), while no cytostatic effect was noted with CyA at a lower concentration (10(-9)-10(-7) mol/l).(ABSTRACT TRUNCATED AT 250 WORDS)