The nucleolar volume and melanin content of the human locus caeruleus and substantia nigra has been measured in 70 persons of age range new born to 91 years, all of whom were at death free from overt neurological illness. Both cell types show a reduction in nucleolar size with advancing age, which becomes disproportionately larger towards old age. At 90 years of age, the change in nucleolar volume in cells of the locus caeruleus amounts to about 5% whereas cells of the substantia nigra show a loss of 20%. The greater decrease in nucleolar volume in cells of the substantia nigra is attributed to the higher concentration of melanin pigment occurring in these cells at old age, rather than the absolute amount present. This marked decline in nucleolar volume in cells of substantia nigra indicates a reduced activity in the cell which, in turn, may be reflected in the difficulty in control and coordination in muscular activity commonly seen in normal elderly persons.