The number of nerve cells was counted in locus caeruleus, dorsal motor vagus, dorsal tegmental nucleus and substantia nigra and the volume of their nucleolus measured in 30 patients with Alzheimer's disease ranging from 48-92 years of age and in 67 control patients without neurological disease. Loss of nerve cells and reduction in nucleolar volume was greatest in the locus caeruleus and these changes were most severely expressed in the younger patients, falling with age such that by 90 years of age the level of damage approached that of old age alone. Less extensive changes were present in the dorsal tegmental nucleus and these were also age dependent in their severity. Moderate damage to the dorsal motor vagus was not age related. Nucleolar volume alone was altered in substantia nigra and then only significantly so in the younger patients.