Background:The aim was to determine the phagocytic activity of thrombocytes in patients with gastric cancer and to assess the effect of oral and parenteral preoperative glutamine-based immunonutrition on nutritional status, thrombocyte phagocytic activity and early postoperative outcomes. Methods:Patients suffer from invasive gastric cancer had been treated with preoperative immunonutrition with glutamine and they were compared to patients without nutritional treatment. Nutritional status, percentage of weight loss and BMI were assessed. Levels of total protein, albumin, cholesterol, triglycerides, platelets and their phagocytic ability were measured twice. Postsurgical complications were assessed via Claven-Dindo classification. Results:Group I-20 patients with an oral glutamine, Group II-38 patients received an intravenous glutamine. Group III-25 patients did not receive preoperative immunonutrition. 47% patients Group I, 54% patients Group II and 33% patients Group III were malnourished. In Group I, percentage of phagocytizing platelet (%PhP) was 1.1 pre- and 1.2 postoperatively. Phagocytic index (PhI) was 1.0 and 1.1. In Group II, %PhP was 1.1 and 1.2. PhI was 1.0 and 1.1. In Group III %PhP was 1.0 and1.2. PhI was 1.0 and 1.1. An increase in triglyceride level was observed in both immunonutrition groups. There was a fall in total protein, albumin level in Group II. In Group III there was a decline in total protein, albumin and cholesterol level. Total platelet count, and PhI was increased in both immunonutrition groups. There was also a rise in %PhP in Group II. In Group III there was no change in blood plateles level, %PhP and PhI. Complications rate was 53% in Group I, 29 % in Group II, 40% in Group III. Conclusions:In invasive gastric cancer, laboratory nutritional parameters are significantly reduced, causing malnutrition in 45.7% of patients. Oral glutamine supplementation inhibited the postoperative decline in protein metabolism parameters, however, this did not affect the reduction of the percentage of postoperative complications. Glutamine used preoperatively significantly reduced the percentage of serious surgical complications, regardless of the way it was supplemented. Patients with invasive gastric cancer have a significant decrease in platelet phagocytic activity. Immunonutrition based on intravenous form of glutamine allows to improve the phagocytic activity of platelets.