A novel human-voltage-dependent-calcium-channel (VDCC) beta subunit was isolated from a 9-week-old human total-embryo cDNA library. Of the four genes encoding beta-subunit isoforms that have been identified in animal species, this isoform shares strong similarity with the rat and rabbit beta 3-related gene product and is referred to here as H beta 3 subunit. The H beta 3 isoform is the second beta subunit identified in human. Its open reading frame encodes a 482-amino-acid protein with a predicted molecular mass of 54.571 kDa. The H beta 3 mRNA is expressed mostly in brain, smooth muscle and ovary. The gene for the human H beta 3 was specifically localized on chromosome 12q13. The cloned H beta 3 subunit was further expressed in Xenopus oocytes to demonstrate its ability to modulate VDCC activity.