The changes that occur in bone after the death of an animal are important because they control whether the bone becomes a fossil and what information is retained concerning the original biology of the animal. Taphonomic study of two ten-year longitudinal samples of wildebeest bones subjected to natural weathering in Amboseli Park, Kenya, provides evidence for progressive change in both the organic and inorganic components of mammalian bone. These changes correspond to weathering stages described on macroscopic structural features. The bone samples were subjected to well-established techniques of protein extraction from mineralized tissue, protein identification by gel electrophoresis and reactivity to antibodies of noncollagenous proteins, as well as x-ray defractometry of the mineral component. Both adult and juvenile bones show progressive increase in hydroxyapatite crystal size and increased protein degradation over the ten-year period. Noncollgenous proteins persist at their original molecular weight in diminished amounts relative to modern controls. In the study area, 10 years or less of natural surface weathering altered the extractability of collagen, indicating peptide and crosslinking cleavage in this protein. Increased hydroxyapatite crystal size may reflect a tendency of crystals to enlarge in situ once the organic matrix begins to breakdown, without the addition of external minerals. -- CAL