The swelling properties of the anterior and posterior stroma of bovine and rabbit corneas were examined by three different methods. The results show that the posterior stroma can swell more than the anterior stroma. Also, at a given swelling pressure, the posterior stroma is more hydrated than the anterior stroma. In a third experiment it is demonstrated that the posterior stroma is also more hydrated in the living eye. It is concluded that the stroma is not a homogeneous structure. The superficial stroma has different physiological properties from the deep stroma. These differences must be taken into account in theoretical models of corneal deturgescence.