As the morphologic expression of the chondrocytic differentiation pathway responsible for bone development and growth, the growth plate has been investigated extensively in the chondrodysplasias. Unique morphologic abnormalities identified in many disorders have provided insight into pathogenetic mechanisms and have been useful diagnostically and nosologically. Biochemical studies have detected evidence of type II collagen defects in patients having disorders in the achondrogenesis type II-spondyloepiphyseal dysplasias (SED) congenita family of chondrodysplasias. Most promising may be the cell culture systems now being developed for human chondrocytes. Preliminary results suggest that they will allow the cellular and molecular biology of the dysplastic growth plate to be directly analyzed.