The purpose of these studies was to evaluate the relative importance of the C-6 carboxyl group on citrate and of the hydroxyl group on citrate and L-malate analogues. Specific methyl esters of citrate and tricarballylate were synthesized and their structures verified by 1H and 13C nuclear magnetic resonance spectra. The formation of an alpha- or beta-methyl ester markedly reduced the ability of the citrate analogue to be a substrate or inhibitor for the citrate transporter. The hydroxyl group was important only for dicarboxylates and in these compounds, it could not be replaced by a keto group. Stereospecificity was also very important for this transport system. In addition, the intercarboxyl distance appeared to play an important role in determining whether the compound could counter transport with citrate or L-malate.