Ribs from 3 preterm infants, who had died after prolonged intravenous feeding and artificial ventilation, were examined histologically and assessed for the degree of osteomalacia and osteoporosis in cancellous bone of the shaft. A grid counting technique was used. Osteomalacia was noted in all 3 cases but to a lesser degree than in classical vitamin D-deficient controls. Osteoporosis was pronounced in the cases of neonatal rickets, but this was not a feature of the vitamin D-deficient controls. Histological features were similar to those reported in experimental phosphate-deficient rickets and vitamin D-resistant rickets.