The multigene family of human Na,K-ATPase is composed of 5 α-subunit genes, 3 of which were shown to encode the functionally active α1, α2 and α3 isoforms of the catalytic subunit. This report describes the isolation, mapping and partial sequencing of the fourth gene (ATP1AL1) that was demonstrated here to be functionally active and expressed in human brain and kidney. Limited DNA sequencing of the ATP1AL1 exons allowed one to suggest that the gene probably encodes a new ion transport ATPase rather than an isoform of the Na,K-ATPase or the closely related H,K-ATPase.