Rat striatum is examined electronmicroscopically after chronic (90-day) treatment with 5 mg/kg dl-amphetamine injected intraperitoneally. Disorganization of the cytoplasmic organelles is observed in part of the nerve cells as well as disappearance of the dense core vesicles. Axonal terminals have reduced electron density, mitochondria with different degree of disorganization and synaptic vesicles and accumulated in groups. Single smooth and concentrically arranged membranes may be found in some of the boutons. Electron-dense bodies and lipid vacuoles are observed in the cytoplasm of the pericytes. The alterations are considered to be the result of chronic amphetamine treatment.