1. The anterior pituitary is well documented to be under the control of central and peripheral factors that dynamically interact to affect cell-specific modulation of pituitary functions. However, it is becoming increasingly evident that these extrinsic factors work in concert with a variety of local products that exert autocrine/paracrine control on pituitary cells. 2. These factors modulate the activity of their target pituitary cells by altering the synthesis and secretion of cell-specific hormones and by exerting control on the growth and differentiation of cells of this tissue. Included in the list of growth factors and bioactive peptides known to be products of pituitary cells are the activins, possibly inhibins and follistatins. 3. These protein factors play an important role in the local modulation of several pituitary cell types and are crucial for the maintenance of normal follicle-stimulating hormone production and, thus, reproductive function and fertility.