Apparent diffusion coefficients (ADCs) of tissue water were determined in chronic brain lesions of a rat stroke model, stroke-prone spontaneously hypertensive rats and compared with histology. ADCs increased in the order control < edema < gliosis < cyst. The differences between individual groups were statistically significant. The increase in ADC is thought to mainly reflect a relative increase in the extracellular space in brain tissue. ADC values may be a clinically useful parameter for tissue characterization.