To evaluate changes in different parameters of the immune status of colorectal cancer patients before their surgical treatment and to look for a possible impact these parameters could exert on overall survival. Forty patients with histologically confirmed colorectal cancer in stage II (n=22), III and IV (n=18) were eligible for inclusion in the present study. Heparinized venous blood (5 ml) of patients was examined 5 days before surgery. Their preoperative white blood cell (WBC) count was >/=3.0*10(9)/l, hemoglobin >/=10 g/l, and platelets >/=180*10(9)/l. The indices of cellular immunity determined for all of the patients were the following: total leukocyte number, absolute number and percents of total lymphocytes, monocytes and neutrophils. The percentage and absolute number of lymphocytes subsets CD3(+), T-helpers (CD4(+)), T-cytotoxic cells (CD8(+)), immunoregulation index (CD4(+)/CD8(+)), B-lymphocytes (CD20(+)), natural killer (NK) cells (CD16(+)) were measured by immunofluorescence methods. Cox regression analysis showed no dependence of the survival on estimated cellular immunity parameters of colorectal cancer patients in stage II. However, the number of circulating lymphocytes and in particular of T cells and NK cells was an independent prognostic variable for overall survival of stage III and IV patients. Analyzing the dependence of survival on immunological indices of colorectal cancer patients, a significant dependence of survival was determined on the absolute preoperative number of total lymphocytes and lymphocyte subsets (total lymphocytes levels >/=1.2*10(9)/l, >/=CD3(+) >/=0.8*10(9)/l, CD4(+) >/=0.3* 10(9)/l, CD8(+) >/=0.3*10(9)/l, and CD16(+)>/=0.25*10(9)/l). Cox regression analysis showed that higher absolute number of lymphocyte subpopulations may be associated with longer survival of colorectal cancer patients in stage III and IV. This study suggests total number of lymphocytes >/=1.2*10(9)/l, CD3(+) >/=0.8*10(9)/l, CD4(+) >/=0.3* 10(9)/l, CD8(+) >/=0.3*10(9)/l, and CD16(+) >/=0.25*10(9)/l before surgery have a beneficial effect on overall survival of colorectal cancer patients in advanced stages (III and IV) of the disease.