Biochemical data and skeletal histomorphometric measurements are presented for normal rats and for two groups of rats rendered uremic by partial nephrectomy. In one of these groups chronic acidosis was induced by the oral administration of hydrochloric acid. Uremic animals had higher urine calcium excretion rates and lower serum concentrations of vitamin D metabolites than normal rats. Chronic acid loading of uremic rats resulted in hypercalcemia, elevated serum parathyroid hormone concentrations, and a significant loss of trabecular bone in addition to the above changes. greater osteoclast densities and higher resorption surfaces wee seen in the uremic acidotic animals than in the other two groups. The acidotic uremic state induced more potent changes in calcium metabolism and bone structure than uremia alone.