This review documents recent insights into the roles of growth hormone and insulin-like growth factor-I during tooth formation. Hereditarily growth hormone-deficient Lewis dwarf rats and hypophysectomized rats have been used to document the influence of growth hormone on growth of the rat incisor and molar teeth in vivo. Cell population studies using bromodeoxyuridine labeling have shown that growth hormone administration to dwarf rats affects odontogenic cell proliferation in the incisor teeth. Immunohistochemistry, employing well-characterized monoclonal antibodies directed against the hormone, its binding protein/receptor, the growth factor and its receptor, has enabled the location of these proteins to be mapped in the ontogenic sequences of ameloblasts, odontoblasts and cementoblasts. This mapping is consistent with the concept that differentiating odontogenic cells are targets for the hormone and that insulin-like growth factor I is implicated as a secondary messenger in the same differentiating cell populations. The content of predentine and precementum matrices proteoglycans appears to be growth hormone-dependent. The proteoglycans implicated so far are rich in chondroitin sulphate and thus they may also be insulin-like growth factor I (sulphation factor)-dependent. Thus matrix synthesis may be what is principally affected by growth hormone in odontogenesis although no evidence of an effect on enamel matrix synthesis or proteoglycan content has yet been documented.