Primary growth hormone (GH) insensitivity (Laron syndrome) is a hereditary disease due to polymorphic defects in the GH receptor, or in the postreceptor mechanisms, leading to an inability to generate IGF-1. The clinical features and biochemical profiles are indistinguishable from isolated GH deficiency. A diagnostic feature is the lack of rise of serum IGF-1 in response to GH. In most patients growth hormone binding protein is low. Treatment of children with Laron syndrome by biosynthetic IGF-1 accelerates linear growth velocity and head circumference, reduces body fat, and stimulates kidney function.