Although hyperoxia is considered a major risk factor for the development of ROP (4), experimental data and clinical studies have also pointed at other factors. Thus, hypercarbia (4), hypocarbia (5) and hypoxemia (6, 7) have been associated with the development of ROP.At least some putative major risk factors in the development of ROP affect cerebral and ocular blood flow (8,9). Experimental work with adult cats, as well as with newborn lambs and piglets, has shown that hypercarbia influences ocular and cerebral blood flows, although the blood flow response in the retina may differ from that of the choroid (10-12). However, studies on ocular blood flow in the neonate are few (13), and to our knowledge there are no reports on the influence of hypocarbia on ocular blood flow in the neonatal period.Hypocarbia and hypercarbia have opposite effects on cerebral vasculature, hypercarbia increasing cerebral blood flow, hypo-