We have cloned a novel cDNA from human brain which encodes a non-voltage-dependent Na+ channel (BNC1). BNC1 has some sequence similarity (24-28%) with a new channel family that includes subunits of the mammalian epithelial Na+ channel, the Caenorhabditis elegans degenerins, and the Helix aspersa FMRF-amide-gated Na+ channel. Like other family members it is inhibited by amiloride. However, its predicted structure differs from other family members, its discrimination between Na+ and Li+ is different, and in contrast to other mammalian family members, coexpression with other cloned subunits of the family does not increase current. BNC1 has a unique pattern of expression with transcripts detected only in adult human brain and in spinal cord. Thus, BNC1 is the first cloned member of a new subfamily of mammalian Na+ channels. The function of BNC1 as a non-voltage-gated Na+ channel in human brain suggests it may play a novel role in neurotransmission.