Patch-clamp experiments were conducted to study the effects of basal lamina (basement membrane) of preovulatory chicken ovarian follicle on membrane currents in differentiated chicken granulosa cells in a homologous system. The membrane capacitance (measure of total membrane area) was smaller in cells cultured on intact basal lamina than that of control cells. The granulosa cells expressed outward and two inward currents. A small fraction of the cells (3%) expressed only a transient fast-activating and -inactivating inward current carried by Ca²⁺. The majority of the cells, however, expressed a slowly activating and inactivating inward current (carried by Cl) that was superimposed on the transient Ca²⁺ current. All cells expressed an outward current characteristic of the delayed-rectifier K⁺ current. The removal of extracellular Ca²⁺ led to elimination of the slow inward Cl current, indicating that it is a Ca²⁺-dependent Cl current. Both peak amplitude and current density of the inward Cl current were significantly lower in cells cultured on freshly isolated intact basal lamina (or basal lamina stored at 4°C for 12 mo) than those of control cells; however, basal lamina had no significant effect on the density of the outward current. Similar to the observations made for intact basal lamina, solubilized basal lamina suppressed the inward Cl current in differentiated granulosa cells. These data show that homologous basal lamina modulates a Ca²⁺-dependent Cl current in differentiated granulosa cells. These findings provide a partial explanation for the mechanisms that subserve the reported effects of basal lamina (basement membrane) on the metabolic functions of differentiated granulosa cells.