Fifteen men, who had undergone Billroth I gastrectomy and 19 men who had undergone Billroth II gastrectomy were studied with respect to vitamin D and other indices of calcium metabolism. The Billroth I group had hypocalcaemia, raised concentration of serum alkaline phosphatase, and reduced bone mineral content. The same biochemical disturbances were found in the Billroth II group, but bone mineral content was normal. In neither of the groups was found signs of increased bone resorption. The calcium absorption was situated in the lower part of the normal range and the fractional absorption and elimination rates were normal. The 25OHD concentrations in both groups were reduced (p less than 0.05-0.01) and the 1.25(OH)2D concentrations raised (p less than 0.01-0.001). The 1,25(OH)2D concentrations were inversely related to bone mineral content, but directly related to signs of bone turnover and calcium absorption. We suggest that the high 1,25(OH)2D concentration is the result of a compensatory process with the aim of preventing hypocalcaemia.