1. If gastric acid is necessary for the absorption of dietary calcium, the total absence of gastric acid secretion that occurs in pernicious anaemia could result in bone loss. To investigate this, we measured calcium absorption and bone density in 21 postmenopausal women (ages 51-76 years) with pernicious anaemia and in 24 normal postmenopausal women (ages 51-79 years). 2. Relative to the normal women, in the women with pernicious anaemia the bone mineral density of the lumbar spine was decreased by 16% (P less than 0.001). 3. After adjustment for age and body weight, lumbar spine bone mineral density correlated with the serum concentration of group 1 pepsinogens (a group of proteins produced by the gastric fundus) (r = 0.61, P less than 0.01). 4. Despite achlorhydria, the women with pernicious anaemia had normal true fractional calcium absorption and normal serum levels of parathyroid hormone and 1,25-dihydroxyvitamin D. 5. We conclude that gastric acid is not required for the absorption of dietary calcium. Thus, the loss of cancellous bone must be caused by some mechanism yet to be identified.