The adsorption heat of gelatin on AgBr was determined calorimetrically in function of the pH for gelatins with high and low isoelectric point (IEP). The adsorption heat increases for pH-values lower than the IEP and remains constant for the higher pH-values. The differences in adsorption heat are also revealed by competitive adsorption with dyes. The amount of adsorbed gelatin is also strongly pH-dependent. The results obtained completely confirm the hypothesis of Pouradier and Roman concerning the structure of the adsorbed gelatin layer; the first molecules are spread over the AgBr surface so as to form a monolayer. If more gelatin is added a reorganisation of the adsorbed molecules occurs. Segments of one definite molecule are replaced by segments of another one. In this way the quantity of gelatin adsorbed can be multiplied.