In the dogfish stroma the normal hydration was approximately 3·2 mg H2O/mg dry weight-slightly less than the normal value obtained previously for mammalian stroma. At this hydration the swelling pressure was zero. When fluid was removed from the stroma, a swelling pressure was obtained which varied depending upon the composition of the test solution. At a given hydration the swelling pressure was greatest in distilled water and least in solutions of 3·0% NaCl containing 6 mmoles/l of Ca2+ or 6 mmoles/l of Mg2+. In artificial dogfish aqueous humor the stroma also showed reduced swelling pressures, but not so marked as in the divalent cation solutions. Beef stromal discs were used for comparison, but no difference in the swelling pressure-hydration relationship was demonstrated when divalent cations were added to saline bathing media. It was concluded that with no measurable swelling pressure of the dogfish stroma in the normal state, there would be no need for a dehydrating mechanism of any magnitude across the surrounding cellular layers.