Vascular permeability and intravascular space in the rat cerebral cortex and hypothalamus were assessed 5 and 14 days after the production of either right or left hemisphere frontal cortical suction lesions. Rats were intravenously injected with large (dextran, 50,000 kdalton) and small (inulin, 5000 kdalton) molecular tracers and tissue samples were removed for assay after 7 min. Five days following lesions of the right but not left hemisphere, inulin levels in the cortical region posterior and contralateral to the lesion site were significantly higher than control values. Dextran levels were not increased in this region by lesions of either hemisphere. However, both right and left hemisphere lesions led to a significant elevation of inulin and dextran levels (inulin higher than dextran) in the cortex surrounding the lesion site. Fourteen days after lesion of either hemisphere, tracer levels were not elevated over control in any region examined. These results suggest that both right and left hemisphere cortical lesions transiently increase local vasopermeability (and perhaps intravascular space), but that only right hemisphere lesions selectively increase inulin in cortex distant from the lesion site, probably from lesion-induced alterations in cerebrovascular permeability.