The annual rate of bone loss in rheumatoid arthritis (RA) and primary generalized osteoarthrosis (PGOA) was determined by measurement of total body calcium (TBCa). The mean annual rate of bone loss in 24 patients with RA treated with nonsteroidal anti-inflammatory drugs (NSAIDs) alone was 3.4%. This rate of bone loss was not reduced in ten RA patients responding to suppressive antirheumatic drugs (4.3%) or seven patients receiving oral calcium supplements (4.5%). The mean annual rate of loss of TBCa in 19 patients with PGOA was 1.6%, a figure which probably represents age-associated bone loss. The rate of bone loss in PGOA was significantly less than that in RA patients not receiving corticosteroids. The mean annual rate of change of TBCa in 30 RA patients receiving corticosteroids (+0.7%) was significantly less than that in any of the other RA groups despite an initial normalized bone mass which was significantly less than in those RA patients receiving NSAIDs alone. The data supported the hypothesis that bone loss occurred early in the course of corticosteroid therapy and thereafter the drugs might have a protective effect on the loss of bone in RA.