In 57 patients surgically treated for ulcer, we found low 25OHD concentrations, elevated 1,25(OH)2D concentrations, (P less than 0.001), a normal iPTH level, and a not significantly reduced bone mineral content (BMC) measured by single photon absorptiometry. The 25OHD concentrations were highest in patients regularly taking tablets containing vitamin D (P less than 0.05), whereas the 1,25(OH)2D concentrations and the BMC values were not affected by vitamin D intake. The most severe calcium metabolic disturbances were seen in 15 Billroth I resected patients whose BMC was 89.4 +/- 12.4% of normal. Although the dietary intake of calcium and vitamin D complied with the Scandinavian recommendations and calcium absorption was in the lower part of the normal range, the general state of nutrition appears to influence the bone mass of such patients. In the patients as a group, the 1,25(OH)2D concentrations were significantly related to BMC (r = 0.44, P less than 0.001) and biochemical signs of bone resorption (r = 0.68, P less than 0.001) and formation (r = 0.42, P less than 0.001) Conversely, no relationship could be detected between serum iPTH and bone mass or bone turnover. We suggest that the high 1,25(OH)2D concentrations found after gastric resections express a compensatory process leading to an increase in calcium absorption, and that the initial event in this sequence is a trend toward low serum calcium levels. With increased demands on this regulation or lack of precursor for 1,25(OH)2D synthesis, bone mass declines through the action of 1,25(OH)2D and/or PTH.