SummaryOsteocyte lacunae were measured in normal rats and in rats in which periosteal hypertrophy had been induced at the adductor longus-pectineus insertion. Lacunae in the cortex beneath the periosteal hypertrophy were significantly larger than lacunae in the cortex of the opposite side of the femur from the hypertrophy. Lacunae in both sides of the femoral cortex of experimental rats were significantly larger than lacunae in the cortex of normal femur. This supports the view that the osteocyte is capable of resorbing bone.