Peroral application of caffeine or theophylline causes a significant increase of the free fatty acids and the free glycerol of the serum; blood sugar and cholesterol are not influenced. FFA and free glycerol decrease during the day by food intake, blood sugar and triglycerides rise. The ingestion of coffee (1-3 cups) does not influence fat and carbohydrate metabolism. To induce a significant increase of lipolysis and of serum triglyceride levels high caffeine doses (1000 mg) are required. Summarizing the data presented, the authors conclude that coffee intake (at dosages compatible with normal nutrition) does not deteriorate glucose tolerance and does not interfere with the fat metabolism. Our findings are confirmed by epidemiologic investigations which have shown that coffee intake is no risk factor for myocardial infarction.