The antitumor activity of subtherapeutical dose of cisplatin and vitamin C combinations was studied against murine Dalton's lymphoma in vivo. The sequence-dependent synergistic antitumor effect of vitamin C and cisplatin was shown to lead to the regression of the tumor resulting in a significant increase in the host survivals with tumor free hosts. Decrease in tumor pH noted in the treated tumor bearing mice and involvement of host's immune system could be an important step in this sequence-dependent antitumor activity of vitamin C and cisplatin.