Background. Postoperative muscle protein catabolism reflected by diminished muscle protein synthesis, reduced glutamine levels and increased nitrogenlosses has in many studies been shown to be reduced by the addition of growth hormone and by the addition of glutamine. The combination of growth hormone and insulin like growth factor (IGF-I, a growth factor which may explain some of the effects of growth hormone) and the addition of glutamina together with growth hormone has so far not been studied postoperatively on muscle protein metabolism. This was the aim of this study. Patients and methods. Metabolic healthy patients undergoing elective colonic resection because of non-spread colonic malignancy were included in the study. The patients were preoperatively weight stable and their BMI were within the normal range. They were given isocaloric (28 kcal/kg/24h) and isonitrogenous TPN (0.15 gN/kg/24h) during 3 days following operation. In three groups TPN was given as a continuous infusion during the study. One group served as a control group (n = 10), another group was given GH postoperatively (GH; n = 7) twice a day subcutaneously (0.15E/kg/injection) and a third group (GH-IGF-I, n = 9) was given the same amount of GH and IGF-I twice a day (40mikrog/kg/24h). Two other groups were given glutamine-containing TPN (0.28g glutamine/kg/24h) during 3 days postoperatively either with addition of growth hormone (GH-GLN; n =8) at a dose of 0.3E/kg/24h, or without growth hormone (GLN; n = 8). In the latter two groups the patients were given TPN during 16 hours per day. Preoperatively and on the third postoperative day a muscle biopsy was taken for analysis of muscle amino acids and determination of the ribosomal patttern reflecting protein synthesis. Urine was sampled during the whole study and the cumulated nitrogen balance was calculated by measuring the total nitrogen content in urine, estimating the extrarenal losses to be 1.5g per day. Results Postoperatively the muscle glutamine was reduced with 22.9 ± 5.6 96 in the control, in the GH group with 22.6 ± 6.5 % and in the GH-IGF-I group with 22.2 ± 4.5 %, all groups given continuous Pn during the study the muscle glutamine level unaltered while a 47.5 ± 6.3 % decline was seen in the GLN group. The concentrations of polyribosomes and ribosomes decreased in a similar way by about 30 % in the control group, in the GH-group and in the GH-IGF-I group indicating a decrease in protein synthesis postoperatively. However, these parameters were unchanged in the two groups given glutamine either with or without growth hormone. In the groups given continuous nutrition during the postoperative period the cumulated nitrogen balance was positive, 6.8 ± 1.6g in the control group, 10.7 ± 1.3 in the GH group and 9.4 ± 2.8 in the GH-IGF-I group. The combination of GH and glutamine reduced nitrogen-losses compared with glutamine alone, -5.8 ± 1.4g vs - 10.6 ± 1. 1g. The two latter groups were not given PN continuously. Conclusion The combination of GH and IGF-I did not in this study improve the parameters reflecting postoperative protein catabolism when PN was given continuously. In both groups a decrease in muscle glutamine and ribosome paramenters reflecting a decrease in protein synthesis were seen. When TPN was given continuously without interruption the cumulated nitrogen balance was improved and positive indicating a beneficial effect on nitrogen metabolism. This effect of the administration of nutrition may be of larger importance than the effect of growth factors in high doses. When glutamine is added a synergistic effect with growth hormone is seen on postoperative glutamine levels which were unaltered compared with glutamine administration alone. When glutamine is adcled the decrease in ribosome parameters reflecting protein synthesis is prevented. The continnous infusion of nutrients and thereby optimizing the whole body nitrogen metabolism may explain the results in this study. It is also plausible that when the metabolid response to trauma is marginal the effects of th