The development of L1210 leukemia transplanted i.v. into CDF1 or BDF1 mice was not affected by pustulan. However, pustulan combined with adriamycin improved the final antitumor effect. The potentiation of the antitumor action was observed when the pustulan administration preceded by 15-8 days the adriamycin injection. The results indicated that the antitumor activity of the pustulan and adriamycin combination was proportional in a range of adriamycin doses (5-10 mg/kg) to the activity of adriamycin by itself. The enhanced tumor-inhibitory effect was accompanied by severe toxicity. Hence, the combination of pustulan with high doses of adriamycin i.e., 20 mg/kg, did not give further prolongation of the survival time of mice over that produced by adriamycin alone. The same relationships were observed when low (10(2) cells and high (10(6) cells) inocula of L1210 cells were grafted into both CDF1 and BDF1 mice.