We have isolated and characterized a human cDNA (HBK2) that is homologous to novel member (RCK2) of the K+ channel RCK gene family expressed in rat brain. RCK2 mRNA was detected predominantly in midbrain areas and brainstem. The primary sequences of the HBK2/RCK2 K+ channel proteins exhibit major differences to other members of the RCK gene family. The bend region between segments S1 and S2 is unusually long and does not contain the N-glycosylation site commonly found in this region. They might be O-glycosylated instead. Functional characterization of the HBK2/RCK2 K+ channels in Xenopus laevis oocytes following micro-injection in in vitro transcribed HBK2 or RCK2 cRNA showed that the HBK2/RCK2 proteins form voltage-gated K+ channels with novel functional and pharmacological properties. These channels are different to RCK1, RCK3, RCK4 and RCK5 K+ channels.