In 254 patients of a ward for infectious diseases the authors demonstrated that inflammatory diseases are frequently accompanied by an increase in nitrate content of the blood, urine and saliva. This effect is especially evident in gastrointestinal disorders. Correlations of nitrate with indicators of the inflammatory process are, if at all, very weak. The endogenous synthesis of nitrate may be of importance for the total nitrate load to the organism especially in children or patients with long-lasting inflammatory disease.