Urine dissolved oxygen (DO) was measured in 40 healthy subjects and 115 patients divided into 4 groups according to their disease. Group 1 (20 patients) had lower urinary tract infection (UI), Group 2 (30 patients) had urinary stone disease (USD), Group 3 consisted of 50 end-stage chronic renal failure patients (CRF) and 15 patients in Group 4 were affected by influenza viral infection (IVI). Urinary and arterial PO2, PCO2 and pH were also measured in 20 healthy subjects. The other 20 healthy volunteers were subjected to submaximal exercise and afterwards urinary DO was estimated. Results revealed that in healthy subjects urinary DO or PO2 is not correlated with urinary pH or arterial pH, PO2 and PCO2. Also, urinary DO did not significantly vary on consecutive days. Urinary DO reflects mainly the renal metabolic state, being increased in conditions of decreased kidney metabolism such as CRF. Submaximal physical exercise, fever or urinary tract infection may significantly reduce urinary DO, whereas DO remains unaffected in uncomplicated USD. Human urinary DO is related to serum creatinine and urine volume. Our results indicate that urinary DO may be a useful indicator in clinical practice.