THE RECURRING CYCLE of ovarian folliculogenesis entails replication as well as differentiation of the developing granulosa cell. Although the central role of gonadotropins in the regulation of granulosa cell ontogeny is well established (1), the variable fate of ovarian follicles subjected to comparable gonadotropic stimulation suggests the existence of additional intraovarian modulatory mechanisms (2). In part, intraovarian control is likely exerted by means of local steroidal modulation (3). However, intraovarian peptides may also have a potential for local modulation of follicular development (4, 5). In this connection, the role of several growth factors has been the subject of increasingly intense investigation. Among potential modulators of granulosa cell ontogeny, the insulin-like growth factors (IGFs) appear uniquely suited to the task, combining replicative and in some instances cytodifferentiative properties. Such duality of action is best exemplified by somatomedin-C (Sm-C)/IGF-I which not only stimulates cell replication in tissues of diverse origin (6) but also promotes the differentiation of cells such as chrondrocytes (7), myoblasts (8), and osteoblasts (9). Although the pertinence of IGFs to granulosa cell physiology has received relatively limited attention, substantial experimental observations now support such possibility. It is the objective of this communication to summarize the information pertinent to the existence of novel intraovarian autocrine control mechanism(s) wherein IGFs may serve as the central signal, and the granulosa cell as their site of production, reception, and action.