For rabbit jejunal brush border vesicles an 'imino carrier' has been defined as a sodium-depedent, alanine-resistant transporter of cyclic imino acids, while for intact rabbit jejunal and ileal epithelia an 'imino acid carrier' has been defined as a sodium-dependent transporter of both aliphatic and cyclic imino acids. This study on intact rabbit intestine examines whether these two terms describe the same epithelial function. The K 1 2Pro and the KiPro against Jmc MeAIB are identical and so are K 1 2MeAIB and KiMeAIB against JmcPro. Likewise, KiLeu is tha same against the transport of both proline and MeAIB. Is is, therefore, concluded that the terms 'imino carrier' and 'imino acid carrier' describe the same epithelial function: A sodium-dependent, relatively high afinity, saturable transporter of both aliphatic and cyclic imino acids. Estimates of the apparent affinity and inhibitory constants for MeAIB, proline and leucine confirm that the jejuno-ileal variation of amino acid transport along the rabbit small intestine is a variation of maximal transport capacity.