The newly emerged Maf family proteins possess a highly conserved basic leucine zipper (bZip) domain in common and are subdivided into large and small Maf proteins. The Maf family proteins appear to regulate cell differentiation processes and also cellular functions as partner molecules of CNC family proteins. To facilitate understanding of the function of small Maf proteins, we isolated the genes (MAFG and MAFK) encoding human small Maf proteins MafG and MafK and characterized their structures and organization by means of restriction enzyme mapping, Southern blot hybridization and nucleotide sequence analysis. Organization of the small maf genes are highly conserved in vertebrates, suggesting an important functional contribution of the gene products. We also examined the location of these genes within the human genome by fluorescence in situ hybridization (FISH) analysis. Human MAFG and MAFK are located at 17q25 and 7p22, respectively. Thus, small maf genes are not clustered in a single locus.