A comparison was made of the effects of two intravenous regimens for postoperative total parenteral nutrition, namely, a conventional (control) regimen (group I) and a single-solution regimen of the same composition (group II). The effects examined were: hemoglobin concentration, prothrombin time, serum protein and electrolyte concentrations, and nitrogen and electrolyte balances. The 18 patients undergoing abdominal surgery were allocated at random to the two groups and the experiment was run for 3 days. During the day of the operation and the next 3 days both groups showed a decrease in the hemoglobin concentration and in the serum levels of iron, albumin, transferrin and cholesterol, while the asparagine aminotransferase increased. During total parenteral nutrition the prothrombin time and erythrocyte sedimentation rate increased in both groups. The nitrogen balance improved gradually in both groups and on the 3rd day was positive in group II. The calcium and magnesium balances indicated a higher retention and the phosphate balance a lower retention of these ions in group II than in group I. The urinary phosphate excretion rate during total parenteral nutrition decreased in both groups. This study indicates that the single-solution regimens used in intravenous nutrition caused no adverse metabolic effects and was used as efficiently as a conventional regimen in the early postoperative period.