Complementary DNAs representing three voltage-gated K(+) channels from humans (HuKI, HuKII, and HuKIV) were isolated, their nucleotide sequences determined, and their functional products examined electrophysiologically. The three human K(+) channels are closely related to the Shaker gene of Drosophila and possess several canonical structural features including multiple hydrophobic segments which are potentially membrane spanning, a positively charged S4 segment which may be the voltage sensor, and a leucine heptad repeat which may be involved in channel gating. Members of the human gene family have specific, highly conserved homologs in rodents, suggesting that the individual members arose prior to the mammalian radiation. The degree of homology indicates that these are among the most highly conserved proteins known. The three human channels expressed in Xenopus oocytes vary in voltage dependence, kinetics, and sensitivity to pharmacological blockers of K(+) channels. HuKII is a rapidly inactivating channel; HuKI and HuKIV are noninactivating. Also, although all three channels are sensitive to the K(+) channel blocker, 4-aminopyridine, only HuKI has tetraethylammonium sensitivity; only HuKIV has charybdotoxin sensitivity. Differences are observed between the pharmacological sensitivities of human channels and the reported sensitivities of their rat homology.