Zinc is an important trace metal co-factor for many metallo-enzymes and may have a critical role in the stabilization and function of biomembranes. Zinc-depleted animals increase their fractional absorption of zinc to restore zinc homeostasis. This increase in fractional absorption is not currently known to be hormonally-mediated. Recently, zinc has been shown to suppress the output of prolactin from dispersed pituitary cells in vitro at physiologic concentrations. Clinical states associated with a tendency to zinc deficiency are also associated with a tendency to hyperprolactinemia. These observations are consistent with the hypothesis that prolactin regulates the uptake and distribution of zinc and that zinc suppresses prolactin in closure of a negative feedback regulatory loop.