The aim of this study was to evaluate the influence of cellular immunity parameters on overall survival of colorectal and gastric cancer patients after surgery. The parameters of cellular immunity (CD3+, CD4+, CD8+, CD20+, and CD16+) were determined by immunofluorescence method. Cox regression analysis showed no impact of the estimated preoperative and postoperative parameters of cellular immunity on overall survival of colorectal cancer patients and similarly of gastric cancer patients in stage II. However, the analysis showed that the survival of colorectal and gastric cancer patients in stage III depended on immunological parameters determined before surgery: CD3+ (P=0.007 and P=0.007, respectively), CD4+ (P=0.021 and P=0.011, respectively), and CD8+ (P=0.047 and P=0.007) counts. Only the survival of colorectal cancer patients depended on natural killer cell number (P=0.009). Kaplan-Meier analysis showed that patients with stage III colorectal and gastric cancer had better survival rates when absolute number of CD3+ lymphocytes, determined before surgery, was greater than 0.8 x 10(9)/L, CD4+--greater than 0.25 x 10(9)/L, CD8+--greater than 0.3 x 10(9)/L. Colorectal cancer patient survived longer when the number of natural killer cells CD16+ was more than 0.25 x 10(9)/L. This study suggests that higher levels of the absolute number of lymphocyte subsets before surgery have a beneficial effect on overall survival of gastric and colorectal cancer patients in stage III.