Food intake and nutritional status was studied in 67 patients, who had had a gastrectomy 2-30 years earlier, and in a randomly selected, matched group of healthy persons. The gastrectomized patients weighed less than the control persons (women 56.4 +/- 9.5 vs 61.4 +/- 6.9 kg; P less than 0.05; men 72.4 +/- 12.5 vs 77.7 +/- 9.2 kg; P less than 0.02). Compared to the controls the gastrectomized women had a significantly lower fat-free mass (37.8 +/- 4.1 vs 40.7 +/- 4.3 kg; P less than 0.02), whereas the gastrectomized men had a lower fat mass (17.0 +/- 7.8 vs 21.2 +/- 6.0 kg; P less than 0.01). The serum concentration of alkaline phosphatase was raised and the concentration of calcium, phosphorus and 25-hydroxycholecalciferol reduced in the gastrectomized group. None of these results could be explained from the nutritional study as both the intake of energy and protein and the intake of calcium and vitamin D was about the same in the operated and the healthy controls. The serum concentration of 25-hydroxycholecalciferol was significantly higher in the gastrectomized persons taking supplementary vitamin D (21.9 +/- 12.0 vs 11.7 +/- 6.5 ng/ml). A daily supplement of 10 micrograms of vitamin D secured normal serum values. As the serum level of 25-hydroxycholecalciferol is correlated to the degree of osteomalacia, all gastrectomized patients should have at least 10 micrograms vitamin D as a supplement once a day.