Sustained subcutaneous administration of recombinant DNA-derived insulin-like growth factor II to immature female hypophysectomized rats stimulated significant increases in body weight gain, tibial epiphyseal cartilage width, femur hydroxyproline concentrations and a significant decrease in serum urea nitrogen concentrations. Recombinant DNA-derived human growth hormone (Humatrope), administered in the same manner produced similar biological effects. The data support the contention that hIGF-II has anabolic effects when administered to hypophysectomized rats and may be a locally acting mediator of pituitary hormone actions.