The gating properties and current amplitudes of mammalian voltage-activated Shaker potassium channels are modulated by at least two associated beta subunits (Kv beta 1.1 and Kv beta 1.2). The human Kv beta 1.1 gene (KCNA1B) resides on chromosome 3, as indicated by somatic cell hybrid mapping. More precise localization of KCNA1B to 3q26.1 was obtained with fluorescence in situ hybridization (FISH) and was corroborated by PCR screening of the CEPH YAC library. The human Kv beta 1.2 gene (KCNA2B) resides on chromosome 1, as indicated by somatic cell hybrid mapping, and has been localized by FISH to 1p36.3.