1. Discs of bone from two fixed sites on the front of the femur were taken from ninety-one necropsy subjects and the density, width and histological appearance of the cortical bone were examined.

2. Cortical thickness, and the density of the femoralcortex, decreased with increasingage of bone.

3. There was an increase in the rate of resorption of the bone cortex from both sexes after the fifth decade.

4. The difference between the density of the metaphysial cortex and that from the diaphysis increased for both sexes after the age of fifty, because of the greater metaphysial resorption.

5. There was no change in the degree of mineralisation of the cortical bone with age. The decrease in density with age is, therefore, accounted for by resorption.