1. The proteins: egg albumin and bovine plasma albumin exert a significant influence on the action of oestrone upon the vagina, but they differ in the concentrations required to produce an effect. Egg albumin does so only in 1·0 % solutions, while plasma albumin is effective in 0·01 % solutions. 2. β-Lactoglobulin may have an effect similar to that of egg albumin. 3. Globulins, fibrinogen, and pepsin have no influence on the action of oestrone upon the vagina. 4. While 1% egg albumin causes a significant alteration only in the position of the dose-response line, 0·01% plasma albumin, in addition, depresses the slope. 5. The significance of these results in relation to (a) the intravaginal dose-response line, and (b) the physical interaction of proteins and oestrogens is discussed.