Infants with sudden infant death syndrome have higher hypoxanthine (Hx) concentrations in their vitreous humor than infants with respiratory distress syndrome and other infant control populations. However, previous research on piglets and pigs applying continuous hypoxemia has not been able to reproduce the concentrations observed in infants with sudden infant death syndrome. To test whether intermittent hypoxemia could, in part, explain this observed difference, Hx, xanthine (X), and uric acid were measured in vitreous humor, urine, plasma, and cerebrospinal fluid in newborn piglets during intermittent hypoxemia (IH) or continuous hypoxemia (CH) of equal degree and duration. Urinary Hx excretion was significantly higher (p < 0.04) in the IH group after 60 min of hypoxemia. The vitreous humor Hx increase was significantly higher in the IH group (from 21.0 +/- 7.8 to 44.1 +/- 25.5 mumol/L, p < 0.01 versus baseline) than in the CH group (from 16.4 +/- 4.2 to 23.2 +/- 7.3 mumol/L, p < 0.05 versus baseline) (p < 0.05 IH versus CH). X increased significantly more (p < 0.05) in vitreous humor in the IH group than in the CH group. No differences between the two groups were found in plasma and cerebrospinal fluid for either Hx, X, or uric acid. We conclude that vitreous humor Hx and X increases more during IH than during CH.