Sleep-associated hypoxemia may result in tissue hypoxia and increased production and excretion of adenosine triphosphate (ATP) degradation intermediates and uric acid. Urinary uric acid:creatinine(UA:Cr) ratio is a convenient method for estimating uric uric acid excretion. We measured the overnight changes in urinary UA:Cr ratio in 17 patients with documented sleep-associated hypoxemia, 13 control patients who remained normoxemic during polysomnography, and 14 normal volunteers. The urinary UA:Cr ratio increased overnight in patients with sleep-associated hypoxemia (+31.2 +/- 10.9%), whereas it decreased in the control patients with negative sleep studies (-13.6 +/- 4.6%; p less than or equal to 0.01) and in the normal volunteers (-23.2 +/- 5.8%). Repeat polysomnography revealed interval resolution of sleep-associated hypoxemia in 2 patients and significant improvement in a third. In every case, this clinical improvement was accompanied by a decrease in the overnight change in UA:Cr ratio. We report that urinary UA:Cr ratio increased overnight in a nonhomogeneous group of patients with sleep-associated hypoxemia.