Excessive intravenous calorie intakes have been shown to increase fat deposition and CO2 production with deleterious results. A controlled trial has therefore been performed to determine whether there is clinical benefit from tailoring calorie intake of intravenously fed patients to the patient's metabolic expenditure. Twenty patients requiring intravenous feeding after abdominal surgery were randomly allocated to receive either (i) a constant regimen containing 2 600 calories and 15.55 g nitrogen or (ii) a varied regimen with a fixed calorie: N2 ratio of 167:1 but with the calorie intake adjusted according to the previous day's metabolic expenditure. Only one patient had a requirement of greater than 2 600 calories; there was no difference in mean RQ during intravenous feeding between the constant regimen (0.90 +/- 0.10 s.d.) and the varied regimen (0.90 +/- 0.09 s.d.) and no significant difference in peak CO2 production. Excess calorie intake over expenditure did not correlate with increased positive nitrogen balance but on the varied regimen patients receiving a higher nitrogen intake tended to be in more positive nitrogen balance. This study suggests that a fixed calorie intake of 2 600 calories per day is suitable for adult patients requiring intravenous feeding after abdominal surgery but currently prescribed nitrogen intakes may be suboptimal.