The growth properties of single-tumor-cell suspensions prepared by enzymatic digestion of solid tumors from Morris hepatomas 7777, 5123tc, and 3924a and the presence of tumor-specific transplantation antigen for tumor lines 7777 and 3924a were described. Two of the tumor cell lines (7777 and 3924a) showed consistent i.m. tumor growth following the inoculation of 1 x 10(5) tumor cells, and a similar dose of 5123tc tumor cells resulted in inconsistent tumor growth. Two of the tumor lines (5123tc and 7777) were associated with rapid appearance of lung metastases, whereas with line 3924a metastatic lung lesions rarely developed despite its rapid i.m. tumor growth rate. Tumor resistance to rechallenge with a threshold inoculum of tumor cells was present in approximately 15 to 50% of the animals following amputation of an existing tumor mass. Resistance to a challenge tumor cell inoculum could also be accomplished by immunization with irradiated tumor cells. Tumor-specific resistance was demonstrated to tumor line 3924a in that "immune" animals were able to resist a challenge with 3924a tumor cells but did not resist a challenge with tumor line 9098.