Voltage-dependent Shaker-related (Kv1) K⁺ channels are composed of transmembrane α subunits and peripheral Kv β proteins that exist as octomers with (α)₄(β)₄ stoichiometry. Although several α (designated Kv1.X) and three Kv β subunits are known to be expressed in brain, their oligomeric combinations in neurons have yet to be deciphered. Herein, the subunits comprising a number of neuronal K⁺ channels from bovine brain cortex were deduced by immunoprecipitation and Western blotting, using antibodies specific for Kv1.X and Kv β subtypes. Only a subset of the theoretically possible oligomers was detected, showing that the synthesis and/or assembly of these multisubunit K⁺ proteins is controlled to yield a limited variety of K⁺ channels. Except for a small population of Kv1.4 containing K⁺ channels, all the recognizable species contained Kv1.2 and β2 subunits. Furthermore, several subpopulations were identified including a fully defined complex of Kv1.2/1.3/1.4/1.6 and Kv β2, plus oligomers containing three or two assigned α subunits. Kv1.2 was also shown to occur in the absence of these other subunits as a putative homo-oligomer. Thus, for the first time, the complete subunit combination of an authentic K⁺ channel has been elucidated; also, the strategy employed to establish this can now be applied to closely related members of other K⁺ channel families.