Abstract.18 patients with intermittent claudication were studied to find some explanation for the beneficial effect of physical training on their symptoms. The patients were randomly allocated to a training group and a placebo‐treated control group. The effect of treatment on serum lipids, muscle lipids and glycogen, walking tolerance, calf blood flow, muscle succinic oxidase activity and thein vitroincorporation rate of glucose‐carbon into various metabolites were studied.In the control group none of these parameters were changed.In the trained group the following significant changes were found: Walking tolerance improved; muscle contents of cholesterol and phospholipids increased, as did succinic oxidase activity and the incorporation rate of glucose‐carbon into glycogen, lipids and carbon dioxide. Incorporation of glucose‐carbon into lactate decreased.The improvement in walking tolerance was correlated with the altered pattern of metabolic activity but was not associated with increased calf blood flow. It is concluded that metabolic changes in skeletal muscles may be important in explaining the beneficial effects of physical training in patients with peripheral arterial insuff