An experimental study has been made of the adsorption of gelatin from solution at 37°C. by collodion membranes. In the case of membranes of high permeability, very high concentrations of gelatin were required to produce maximum adsorption, and the maximum amounts adsorbed were independent of the pH values of the solutions over the range 3.8 to 4.8. With membranes of low permeability, maximum adsorption was reached at lower gelatin concentrations, and the maximum amounts adsorbed varied with the pH, being lower on either side of the isoelectric point, over the range 3.8 to 6.6. The addition of salt in such experiments raised the maximum amount adsorbed to a value equal to that obtained with solutions at the isoelectric point in the absence of salt. These experiments can be explained by, and seem to lend support to, the theory proposed by Loeb and further developed by Kunitz concerning the effects of pH and salt on the size of gelatin particles in solution.