The pulmonary vascular tree undergoes remarkable postnatal development. While studies have characterized longitudinal changes in vascular function with growth, none have explored regional patterns of vascular remodeling. We studied 6 pigs to see how regional blood flow changes with growth. We selected pigs because of their rapid growth and similarities to human pulmonary vascular tree development. Fluorescent microspheres were injected into the pulmonary circulation to mark regional blood on days 3, 12, 27,43,and 71 after birth. The animals were awake and prone for all injections. The lungs were subsequently removed, air dried, and sectioned into ~ 2 cm(3) pieces. Flow on each injection day was determined for each piece. Despite the increase in the hydrostatic gradient in the lung with growth, there was a strong correlation between blood flow to the same lung piece when compared on days 3 and 71 ( 0.73 +/- 0.12). Although a dorsal-ventral gradient of perfusion did not exist on day 3, blood flow increased more in the dorsal region by day 12 and became more uniform by day 71. Although most of the lung pieces did not show a discernable pattern of blood flow redistribution, similar spatial patterns of blood flow redistribution existed across animals. Our findings suggest that local mechanisms, shared across animals, guide regional changes in vascular resistance during postnatal development. In the pig, these mechanisms act to produce more uniform flow in the normal posture for an ambulating quadruped. The stimuli for these changes have not yet been identified. Key words: blood flow distribution, remodeling, vertical gradient.