1. Chicken erythrocytes exposed to low concentrations of saponin have their membranes altered.2. By removing the saponin and resuspending the cells in Ringer-Locke, they will remain unhemolyzed for several days, even though the membranes have been altered.3. These cells are more permeable to both lipoid-soluble and lipoid-insoluble molecules.4. The penetration of both types of molecules appears to be affected equally.5. The rate of penetration of a large molecule such as malonamide is increased more by this treatment than the rate of penetration of a smaller molecule such as glycerol.6. The fragility of these cells is not increased by this treatment.