In order to clarify the role of lysosomal enzymes in the developmental mechanisms of cerebral lesions under chronic hypertensive conditions, we histochemically and biochemically investigated acid phosphatase, N-acetyl-beta-glucosaminidase, and cathepsin B in the cerebral cortex and subcortical white matter in stroke-prone spontaneously hypertensive rats (SHRSP). Histochemical investigation showed that SHRSP had an increased number of cells with positive reaction to these enzymes in the edematous cortex and degenerated subcortical white matter. The cells with positive reaction were made up of reactive astrocytes and microglias. The activities of all enzymes in the aged SHRSP were higher than those in normotensive rats, the differences being significant at 24 weeks of age. The present study suggests that chronic hypertension or chronic edema causes increased activities of lysosomal enzymes in the cerebral cortex and subcortical white matter, and that the activated lysosomal enzymes take part in the developmental mechanisms of cystic formation as well as the diffuse degeneration of the white matter.