One extensive periosteal stripping of the femur and tibia from one epiphyseal plate to the other in dogs caused some increase in longitudinal growth on the stripped side as compared with the unstripped side in 63 per cent of paired bones. A second stripping operation performed one or two months later produced a statistically significant increase in growth after a single stripping operation in dogs. Two periosteal stripping operations in monkeys caused a slight increase in longitudinal growth in the long bones in 87.5 per cent of the cases. Pathological fractures of the femur or tibia occurred after two stripping procedures in five of the twenty-two dogs and in five of the ten monkeys.