1. The activities of hexokinase, phosphofructokinase, fructose bisphosphatase and 2-oxoglutarate dehydrogenase have been measured in the vastus lateralis and rectus abdominus muscle of normal human subjects and in very ill surgical patients.
2. The activities of these enzymes in the muscle of control subjects were similar to the pattern seen in the skeletal muscle of other mammals and lower vertebrates.
3. Fructose bisphosphatase and phosphofructokinase activities were significantly lower in the muscle of ill patients although the depression of the activity of fructose bisphosphatase was much greater than that of phosphofructokinase in both muscle types of ill patients.
4. The maximum rate of cycling in the fructose 6-phosphate-fructose 1,6-diphosphate cycle may be altered in the ill.
5. This decreased cycling may have a direct influence on the sensitivity of glycolysis to regulators such as the adenine nucleotides and may reduce the ability to maintain body temperature.
6. Increased glycogen synthesis in these muscles may indicate that the role of fructose bisphosphatase is unlikely to be solely in glycogen resynthesis.