ADP-ribosylation factors (ARFs) are a family of small GTP-binding proteins that are proposed to be involved in the formation of coated transport vesicles. Although six ARF sequences have been reported in mammals to date, it has been unclear how many ARF members are present in a single organism. In this study, we provide the first direct evidence by cDNA cloning for the presence of all six ARF members in mouse. These proteins are highly conserved across mammalian species and Northern blot analysis revealed that mRNAs for all the members were expressed ubiquitously. Transfection of cells with epitope-tagged ARFs revealed that ARFs 1-3 displayed a perinuclear Golgi localization, while ARFs 4-6 appeared to be widely dispersed throughout the cytoplasm. These results suggest that although all the ARF proteins play fundamental and critical roles in cellular function, they are involved in different vesicular transport processes.