The two P domain hTRAAK K(+) channel has been cloned from human brain. hTRAAK cDNA encodes a 393 amino acid polypeptide with 88% of homology with its mouse counterpart. The hTRAAK gene has been mapped to chromosome 11q13 and the study of its organization indicates that the hTRAAK open reading frame is contained in six exons. hTRAAK is expressed abundantly in brain and placenta. In COS cells, hTRAAK currents are K(+)-selective, instantaneous and non-inactivating. These currents are insensitive to the classical K(+) channels blockers 4-aminopyridine, tetraethylammonium, barium and quinidine, but are strongly stimulated by application of arachidonic acid as well as other polyunsaturated fatty acids. hTRAAK can also be activated by a stretch of the membrane.