The murine B-lymphocyte differentiation antigen BP-1/6C3 has been identified as glutamyl aminopeptidase (EAP), the gene symbol for which is ENPEP. Using genomic DNA encoding for human EAP as a probe, we identified the ENPEP gene location on human chromosome 4q25 by polymerase chain reaction analysis of a human/rodent somatic cell hybrid mapping panel and by fluorescence in situ hybridization. Using a radiation hybrid panel, the gene order around ENPEP was determined to be centromere-D4S1236-(570 kb)-ENPEP-(210 kb)-D4S262-(270 kb)-D4S953-(270 kb)-D4S474-(570 kb)-IF. The linkage of ENPEP to complement factor I (IF) confirms the human chromosome band 4q25 localization predicted from the chromosomal location of murine ENPEP. Human ENPEP thus provides an additional marker for the long arm of chromosome 4 that should facilitate studies of this genomic region.