Lauric acid reduced osmotic RBC fragility at low salt concentrations and caused hemolysis under normotonic conditions. KCN inhibited the hemolytic effect of l.a. under normotonic but did not influence its action under hypotonic conditions. It is concluded that l.a.-induced hemolysis requires penetration of the f.a. into a deep membrane pool whereas binding of l.a. in the superficial RBC-membrane pool is sufficient to reduce osmotic fragility of RBC at low salt concentrations.