BACKGROUND: Nitric oxide and its metabolites, nitrate and nitrite, are important regulators linked to various diseases. We studied the association of fasting serum concentrations of nitrate and nitrite, combined as NOx, without special diet, with the prevalence of various chronic diseases. METHODS: Fasting concentrations of NOx were assayed in a cohort of 1087 patients recruited to Stress Aging and Health in Russia study that represents male and female population in Moscow, Russia, over 55 years of age. Chronic diseases were recorded based on anamnesis and additional assays were run to characterize immune status and lipid and carbohydrate metabolism Odds ratios were calculated to associate NOx concentrations with prevalence of chronic diseases in pooled deciles below or above borderline. RESULTS: NOx over 44.7 mu M were associated with increased prevalence of various chronic diseases such as diabetes type II, hyperthyroidism, coronary heart disease, gout and thrombosis/stroke. NOx 65.3 mu M and above were associated with lowered prevalence of osteoporosis. NOx levels of 74.6 mu M and above were associated with significantly higher number of patients who abstain from consumption of alcoholic beverages. NOx were not associated with cancer. CONCLUSIONS: Thus, fasting concentrations of NOx in serum can be an important diagnostic parameter characteristic for specific chronic diseases.