Recent data show that in humans IGF-1 has insulin-like anabolic and growth promoting effects. However, the plasma levels at which IGF-1 exerts these effects differ. IGF-1 plasma levels similar to those in normal children and adults have a growth promoting effect, but higher levels are necessary for IGF-1 to exert insulin-like anabolic effects, and hypoglycemia is a potential risk. Longitudinal bone growth results from the proliferation and differentiation of chondrocytes in epiphyseal cartilage. We present our data from cultured human epiphyseal chondrocytes, which suggest that epiphyseal cartilage may be a target tissue for IGF-1 action during human fetal and postnatal development.