Measurements of voluntary hand grip strength (GS) are a sensitive predictor of postoperative complications. The loss of body protein is thought to be important in the development of these postoperative complications, but the relationship between GS and body protein status has not been studied. We have measured GS (by hand dynamometry), total body protein (indirectly by mid-arm muscle circumference, and directly by in vivo neutron activation analysis) and the proportion of protein loss (protein index) in 80 patients with gastrointestinal disease and 87 normal volunteers. Using regression analysis, a matched study and clinical decision analysis, it has been demonstrated that GS is a sensitive measurement of the degree of protein loss. The results support more widespread use of GS measurements in the identification of patients at high risk of postoperative complications and in the monitoring of patient response to nutritional intervention.