The whole-cell patch-clamp technique was used to record outward K+ currents in the human neuroblastoma cell line SH-SY5Y. These K+ currents were inhibited by tetraethylammonium (20 mM) and by 4-aminopyridine (2 mM). The Ca2+ channel blocker Cd2+ (0.2 mM) also inhibited K+ currents, indicating that a component was Ca(2+)-activated. Glibenclamide, a presumed selective inhibitor of ATP-sensitive K+ channels, caused reversible inhibitions of the K+ currents and appeared to accelerate their inactivation. These effects were not significantly affected by intracellular ATP (ATPi), and were observed in the presence of 0.2 mM Cd2+. It is concluded that glibenclamide inhibits a voltage-gated, Ca(2+)- and ATPi-independent K+ current in SH-SY5Y cells.