An initial characterization of the lenticular ionic permeabilities of the isolated Sprague-Dawley rat lens utilizing short-circuiting techniques was carried out to provide the basis for further studies of mechanisms underlying cataractogenesis associated with salt-sensitive genetic hypertension in the rat. Both active and passive Na+and Kftransport were evaluated by varying ionic concentrations in the bathing solutions facing the anterior and posterior sides of the lens, as well as by the addition of BaCb and ouabain. In general, the ionic permeabilities and transport properties of the rat lens are qualitatively similar to those previously described in other species. Ionic replacement studies showed the presence of Nafand K+channels at both surfaces of the lens, with the anterior side K+conductance being larger than the posterior. In contrast, Na+conductance was similar at both lens surfaces. The effects of ouabain confirmed the presence of the Na+ -K+ -ATPase at the lens epithelium, while the effects of serial addition of BaCh and ouabain suggested that the contribution of Kfdiffusion to the short-circuit current may be considerably greater than the electrogenic component of the Na+-K+pump.