A novel human-voltage-dependent-calcium-channel (VDCC) β subunit was isolated from a 9-week-old human total-embryo cDNA library. Of the four genes encoding β-subunit isoforms that have been identified in animal species, this isoform shares strong similarity with the rat and rabbit β3-related gene product and is referred to here as Hβ3 subunit. The Hβ3 isoform is the second β subunit identified in human. Its open reading frame encodes a 482-amino-acid protein with a predicted molecular mass of 54.571 kDa. The Hβ3 mRNA is expressed mostly in brain, smooth muscle and ovary. The gene for the human Hβ3 was specifically localized on chromosome 12q13. The cloned Hβ3 subunit was further expressed in Xenopus oocytes to demonstrate its ability to modulate VDCC activity.