1. Studies on the mineralization of the skeletons Scottish Blackface wethers and breeding ewes have been carried out on three widely scattered and differing Scottish hill farms using field radiography and bone-ash analysis.

2. Regular small autumnal improvements in the density of the ewes' skeletons were detected by in vivo radiography using the right radii although, in general, the radii of the ewes were at all times considered to be in good condition (for Scottish Blackface sheep on the hill) and underwent no marked resorption (as judged from in vivo radiographs) during pregnancy and lactation. This was contrary to what was expected in view of the results of previously reported laboratory experiments (Benzie et al. 1955, 1956, 1959) and also in view of commonly held beliefs that hill pastures are, in general, deficient in calcium or phosphorus, or both of these dietary factors.

3. There were few significant flock differences (both ewes and wethers) for the values assigned to the radiographs or for the results of skeletal ash determinations even though the flocks were maintained in widely separated and differing locations and husbandry systems.

4. It is suggested that further field work along these lines may be of great value to the obtaining of a clearer understanding of the ewe: hill pasture relationship.