The present observations demonstrated that the granulosa cells of developing follicles in the rabbit ovary bind antimyosin-like antibodies (AMA). The same granulosa cells studied with the electron microscope showed bundles of microfilaments in the cortical areas of the cytoplasm and within microvilli and large cellular evaginations. The immunochemical and ultrastructural results suggest that the ovarian follicles are not passive organs, but, containing contractile granulosa cells, are capable of producing "in vivo" discrete movements.