Recently, cDNA cloning and expression of three mRNA variants of the human NSP gene were described. This neuroendocrine-specific gene encodes three NSP protein isoforms with unique amino-terminal parts, but common carboxy-terminal parts. The proteins, with yet unknown function, are associated with the endoplasmic reticulum and therefore are named NSP reticulons. Potentially, these proteins are neuroendocrine markers of a novel category in human lung cancer diagnosis. Here, the genomic organization of this gene was studied by analysis of genomic clones isolated from lambda phage and YAC libraries. The NSP exons were found to be dispersed over a genomic region of about 275 kb. The present elucidation of the genomic organization of the NSP gene explains the generation of NSP mRNA variants encoding NSP protein isoforms. Multiple promoters rather than alternative splicing of internal exons seem to be involved in this diversity. Furthermore, comparison of NSP genomic and cDNA sequences with databank nucleotide sequences resulted in the discovery of other human members of this novel family of reticulons encoding genes.