In a prospective randomized trial in patients undergoing major abdominal surgery, the impact of a new enteral formula supplemented with arginine, omega-3 fatty acids, and nucleotides (A, n = 14) on immunological parameters was compared with a standard enteral formula (B, n = 14) and a low calorie/low fat intravenous solution (C, n = 13). Four days postoperatively, a statistically significant decrease in total leukocyte count (A, 9.0 +/- 2.9; B, 8.0 +/- 2.4; C, 11.1 +/- 3.5 x 10(6) cells/mL; A versus C, B versus C; p < 0.05), higher percentage of lymphocytes (A, 14.3 +/- 4.9; C, 8.2 +/- 6.1; p < 0.05), and decreased median CRP levels (A, 80.4 [69.9]; B, 70 [74]; C, 88.5 [142] in mg/L; A versus C, p < 0.05; B versus C; p < 0.05) were observed in the enteral nutrition groups. The expression of activated surface antigen HLA-DR was diminished on CD14+ cells over 4 d (A, 58.2 [39.2]; B, 52.2 [36.2]; C, 76.6 [25.2] in %; A versus C, p < 0.05; B versus C, p < 0.05) and 8-10 d (A, 37.9 [31.4]; C, 58.5 [37.6]; p < 0.05) postoperatively. Significantly enhanced median phagocytic activity of CD14+ monocytes and granulocytes was observed in group C 8-10 days postoperatively (A, 83.3 [11.8]; B, 71.6 [34.1]; C, 87.4 [10.8]; A versus B, B versus C, p < 0.05; and A, 75.7 [10.0]; B, 69.0 [37.8]; C, 80.0 [10.1] in %, B versus C, p < 0.05, respectively). Postoperative hospital and intensive care unit stay was similar among the three groups; however, infectious complications were less frequent in group A (A versus C, p = 0.15). Thus, a modified enteral nutritional support and supplementation may influence the immune competence toward a more efficient defense response.