The transport characteristics of (1D)chiro-inositol by the ciliate Tetrahymena were examined in competition studies employing [³H](1d)chiro-inositol. (1d)chiro-Inositol transport was competed by unlabeled (1d)chiro-inositol, myo-inositol, scyllo-inositol, and d-glucose in a concentration-dependent manner. Conversely, (1d)chiro-inositol competed for [³H]myo- and [³H]scyllo-inositol transport. Lineweaver-Burke analysis of the competition data indicated a K_m of 10.3 mM and a B_max of 4.7 nmol/min/mg for (1d)chiro-inositol. Transport of (1d)chiro-inositol was inhibited by cytochalasin B, an inhibitor of facilitated glucose transporters, and phlorizin, an inhibitor of sodium-dependent transporters. Removal of sodium from the radiolabeling buffer also inhibited uptake. The presence of 0.64 mM calcium or magnesium ions exerted negligible effects on transport, although potassium was inhibitory. [³H](1d)chiro-Inositol was shown to be incorporated into Tetrahymena phosphoinositides.