OBJECTIVE The question of whether TPN is able to reverse lean body mass depletion in cachectic cancer patients and, in particular, its effect on protein kinetics is a matter of some controversy. This study investigates the impact of TPN on protein kinetics in patients with gastric cancer. METHODS The study involved three patients with 14-30% weight loss. They were administered a TPN regimen including 33-40 kcal/kg/day and 1.4-1.7 g amino acid/kg/day. The protein metabolism was studied before and during TPN using a stable amino acid isotope. RESULTS Whole body protein turnover and breakdown did not change during TPN, whereas whole body protein synthesis increased from 3.39 +/- 1.04 to 6.05 +/- 0.48 g/kg/day (P = 0.03). However, the net balance, which was slightly negative prior to TPN, became positive during nutritional support. In the skeletal muscle compartment the synthesis improved with TPN (from 9.38 +/- 2.6 nmol/100 mL/min to 35.95 +/- 3.4 nmol/100 mL/min; P = 0.0143), whereas breakdown did not change significantly. CONCLUSIONS TPN triggers a positive metabolic response in cachectic cancer patients. Whether this results in a clinical benefit for the patient requires further investigation.