We conducted a randomized double-blind placebo-controlled study evaluating the influence of 5 weeks' duration of 30 g enteral glutamine supplementation on inflammatory and hormonal responses in 73 patients with rectal cancer undergoing preoperative radiochemotherapy. Plasma levels of inflammatory and hormonal parameters were controlled at the beginning and at the end of supplementation. Enteral glutamine resulted in modulation of inflammatory and hormonal responses as shown by a decreased plasma interleukin 6 and cortisol levels in glutamine compared with placebo group: 5.5±3.8 versus 11.1±19.9 ng/l (P=0.02) for IL-6 and 386±168.4 to 312.7±111.7 nmol/l (P=0.03) for cortisol. We conclude that enteral glutamine exhibits some anti-inflammatory activity and, consequently, leads to a lower hormonal stress response during radiochemotherapy in patients with rectal cancer.