Brains from four parkinsonian patients and one control patient were analysed by electron microscopy. The most consistent abnormal findings were nerve fibers rarefaction, great interstitial space enlargement, neuropil disruption, mitochondrial tumefaction and degenerative changes. These findings occurred regularly in the brain of parkinsonian patients. Furthermore, except for mitochondrial changes, they were distinctively absent in the control patient, and therefore cannot be attributed to technical problems. Contrarywise, they clearly reflect chronic neuronal loss. Also noteworthy was the demonstrative of deposits of amorphous substance into mitochondria, axons, cytoplasm and into the interstitial space.