Salinization of the medium inhibits both K(+) uptake by excised barley (Hordeum vulgare L.) roots and K(+) release from their stele, as measured by short-term (86)Rb uptake and xylem exudation, respectively. Although inhibition was not specific to chloride, mannitol caused a different response from that of inorganic sodium salts, indicating that inhibition was at least partly the result of an ion effect. In roots previously exposed to low levels of NaCl, NaCl stress directly affected stelar K(+) release, whereas in low-sodium roots stelar K(+) release was much less salt-sensitive than K(+) uptake.