Complete nitrogen balance studies have been conducted in 17 patients undergoing vagotomy and pyloroplasty during the first 6 post-operative days. All patients received only intravenous nutrition during this period and there were no metabolic complications. These studies have shown that the optimum nitrogen and energy intake in the post-operative period in adults are 0.24 g nitrogen and 46 kcal/kg body weight/day, respectively. These studies throw further doubt on the use of the E/T ratio as a predictor of nitrogen source solution efficiency in intravenous nutrition regimes. It is suggested that more attention should be directed to the non-essential nitrogen constituents in those solutions where the essential amino acid nitrogen contributes 30 % of the total nitrogen. A new solution, Amodex, with an E/T ratio of 2.62 and an essential amino acid nitrogen content of 30 % of the total nitrogen content has been found to compare favourably with two other well-established solutions in the post-operative period. These studies suggest that of the three solutions, Vamin 7 %may be marginally more efficient.