The vasculature provides multicellular organisms with transport routes for nutrients and signalling molecules, and in plant leaves this vital function is provided by the veins. Vein patterning is known to be regulated by the hormone auxin and the auxin transporter PIN1, but it has been unclear where in the leaf PIN1 needs to transport auxin for the hormone to pattern veins. Although the prevailing notion has been that epidermal peaks of PIN1 expression lead to localised transport of auxin into the inner tissues, thereby promoting vein formation, this hypothesis had yet to be tested. Now, Enrico Scarpella and colleagues instead find that epidermal PIN1 expression is dispensable for vein development. When PIN1 is expressed exclusively in inner or vascular tissues, the abnormal vein pattern of pin1 mutants is rescued; by contrast, PIN1 expression in the epidermis or non-vascular inner tissues fails to rescue the mutant pattern. These effects cannot be accounted for by compensation by PIN3, PIN4 and PIN7, even though they are expressed in the epidermis and inner tissues during vein patterning. Therefore, auxin transport in inner tissues, rather than the epidermis, is both required and sufficient for vein patterning.