The CEBPA gene encoding CCAAT/enhancer binding protein (C/EBP alpha) has been mapped to human chromosome 19 and the CEBPB (formerly TCF5) gene encoding NF-IL6 (C/EBP beta) to human chromosome 20 by Southern blot analysis of Chinese hamster x human and mouse x human somatic cell hybrids. CEBPA has been further mapped to 19q13.1 between the loci GPI and TGFB using human x hamster somatic cell hybrids containing restricted fragments of human chromosome 19. This position was confirmed by fluorescence in situ hybridization. Furthermore, CEBPB has been mapped to 20q13.1 by fluorescence in situ hybridization.