The activins and inhibins are structurally-related members of transforming growth factor β (TGFβ) superfamily that selectively stimulate or suppress follicle-stimulating hormone (FSH) synthesis in pituitary gonadotrope cells. According to current dogma, gonadotrope-derived activin B binds to and signals via complexes of activin type II and type I receptors to stimulate transcription of the FSHβ (Fshb) subunit gene. Gonadal inhibins are thought to antagonize activins, and thereby suppress FSH, by forming high affinity ternary complexes with activin type II receptors and the TGFβ type III receptor, betaglycan. Results from our lab challenge these concepts. First, activin B is a homodimer of inhibin βB subunits (product of the Inhbb gene). However, FSH levels are elevated or normal in global or gonadotrope-specific Inhbb knockout mice. Moreover, conditional deletion of the canonical activin type I receptor, ALK4, in gonadotropes does not affect FSH production in vivo. These (and other) results suggest that activin B is not an essential regulator of FSH production in mice. Second, FSH synthesis is unaltered in mice lacking betaglycan in their gonadotropes. When pituitaries of these mice are challenged with inhibin A or inhibin B, only inhibin A’s suppressive actions on FSH production are impaired. These data indicate that betaglycan functions as an obligate inhibin A, but not inhibin B co-receptor in murine gonadotropes. In our ongoing research, we are trying to identify: 1) the TGFβ ligand that stimulates FSH production in vivo, and 2) the inhibin B co-receptor in gonadotropes.