We conducted a controlled, double-blind study of parenteral glutamine supplementation in an unselected group of consecutive autologous transplant patients. Patients received 30 g of alanyl-glutamine dipeptide (Dipeptiven; Fresenius-Kabi, Bad Homburg, Germany) or glutamine-free amino acid solution i.v. from day +1 to day +14 or to discharge. All patients were assessed for clinical status, mucositis, blood counts, oral intake and immune reconstitution. Parenteral nutrition was administered according to predefined guidelines. Forty patients were randomized; 21 into the glutamine and 19 into the placebo arm. Glutamine patients had less days with diarrhoea (3.3 +/- 4.0 vs 4.3 +/- 3.0, P = 0.03), but they had more severe oral mucositis (mean 4 +/- 4.7 vs 1.4 +/- 2.3 days of mucositis score >13, P = 0.04), spent more days on opioids (mean 3.5 +/- 4.2 vs 1.2 +/- 2.2 days, P = 0.03) and left hospital later than placebo patients (mean 13.5 +/- 3.1 vs 11.7 +/- 2.4 days after transplant, P = 0.06). There were more relapses (P = 0.02) and deaths (P = 0.05) in the glutamine group. The cost of supportive care (mean 2960 +/- 1694 vs 1534 +/- 513 Euro, P = 0.002) was also greater for glutamine patients, mainly due to the cost of glutamine dipeptide itself. The described mode and dosage of glutamine administration did not produce meaningful benefit in our autologous transplant patients and it was certainly not cost-effective.