This study examines the glutathione status of red blood cells in patients with retinopathy of prematurity (ROP) both in vivo and after an in vitro oxidative challenge. Fifty ROP patients of different ages (between 6 weeks and 6 years), born prematurely (gestational age: 28.7 +/- 1.3 weeks; birth weight: 1210 +/- 313 g; mean +/- SD) suffering either from active ROP (<3 months old; n = 12) or from a visual handicap due to preceding ROP (3 months-6 years; n = 38) as well as control patients of similar age and maturity (n = 56) were included. Infants with active disease have the lowest levels of reduced glutathione (GSH), the highest levels of oxidized form (GSSG), the highest GSSG/GSH ratios and the greatest fall in GSH after an in vitro oxidative challenge. After an in vitro oxidative stress, defective glutathione recycling was found in patients with preceding ROP and was suggested as a factor predisposing to oxidative hemolysis. The glutathione redox ratio was warranted as a biochemical screen for active ROP in premature infants.