Isoelectric point (pI) distribution of the four types of photographic gelatin and ammonia treated samples have been examined. Isoelectric focusing (IEF) on polyacrylamide slabs in the presence of urea followed by a dye staining gave reproducible results. Each type of gelatin gave characteristic IEF pattern although those of limed gelatins were indistinguishable. Hydrolysis of peptide-backbone with ammonia treatment (amidolysis) was rather slight and the drop of average pI was accompanied not by a uniform shift of pI range but an expansion of pI distribution.