Histological examination of bone from 25 patients with small-intestinal resection showed that 9 (36%) had osteomalacia, which was severe in 5 and mild in 4. The serum-alkaline-phosphatase concentration was raised in all patients with severe osteomalacia, but serum calcium, phosphate, and alkaline-phosphatase concentrations were normal in the 4 patients with mild disease, 2 of whom had symptoms. Osteomalacia was diagnosed radiologically in only 3 patients. Osteomalacia appears to be commoner in patients with small-intestinal resection than has previously been thought, and bone biopsy is essential if all cases are detected. Although high-dose parenteral vitamin-D therapy is usually effective in the treatment of osteomalacia after small-intestinal resection, our findings showed that oral vitamin-D metabolites and their analogues may also be effective. This has important practical advantages.