The distribution of laminin, type IV collagen and fibronectin was studied by immunofluorescence in rat, pig and cow ovarian follicles. The results obtained in the three species investigated were similar. In all the follicles, laminin and type IV collagen were identically localized in the basal lamina (BL) separating the granulosa and the theca layers. In addition, these two proteins were also distributed in the wall of blood vessels of the thecae and ovarian stroma. The staining showed that the BL of primordial and growing follicles was regular and continuous, but underwent striking modifications during ovulation and atresia. In fact, in preovulatory follicles the BL appeared thinner and discontinuous, whereas it was much thickened and ruptured in atretic follicles. Fibronectin was localized mainly in inner granulosa cells of small and medium-sized growing follicles, and as a broad and irregular layer around the cavity of the degenerated follicles. The results show that each stage of follicular growth and involution is associated with a precise and peculiar pattern of distribution of laminin, type IV collagen and fibronectin. The possibility that these proteins play a role in the local control of ovarian follicular dynamics is advanced.