Contemporary knowledge about isoprene in expired breath is summarized and its possible application on metabolic care is discussed. The isoprene formation as a precursor of cholesterol and isoprenoids and depen- dence of its concentration on various diseases, such as hypercholesterolaemia, is described. The concentration of isoprene in the expired breath shows circadian changes similar to physiological changes of cholesterol synthesis.

        Key words: isoprene, cholesterol synthesis, isoprenoids.