['To test the hypothesis that variable supplemental oxygen (VSO) during recovery is not as effective as constant supplemental oxygen treatment at reducing retinal neovascular severity in the newborn rat model of retinopathy of prematurity (ROP).', 'The ROP model consists of raising newborn rats in variable oxygen for 14 days and then allowing them to recover during the next 6 days (until day 20). During this recovery period, two VSO protocols were examined: 1) 24 hr cycled (28% for 24 hr and 21% for 24 hr) as a control, and 2) interrupted (28% for 23.75 hr and 21% for 0.25 hr). On day 20, retinas from both eyes of each animal were dissected, stained with ADPase, and analyzed for neovascular (NV) incidence, severity, and peripheral avascularity.', 'No significant differences (P > 0.05) in NV incidence and severity were found between the 24 hr cycled (control) (95% (38/40), median 5 clockhrs, range 0.5-9, n = 38) and interrupted VSO groups (89% (40/45), 3.5 clockhrs, 0.5-10.5, n = 40). However, retinal NV severity from both VSO groups were significantly greater (P < 0.05) than that previously reported for constant supplemental oxygen treatment. Percent peripheral avascularities were not significantly different (P > 0.05) between the two VSO groups.'] Does variable supplemental oxygen during recovery reduce retinal neovascular severity in experimental ROP?