Serum isoamylases with alpha-glucosidase activity from cattle, sheep, horses, goats, red deer, pigs and dogs were compared to one another. 2. The isoamylases from cattle and pigs were polymorphic. 3. In agarose gel electrophoresis the isoamylases behaved as alpha-1-globulins but in starch gel electrophoresis they were differentially retarded by affinity effects. 4. Molecular weights were estimated: cattle (417,000); sheep (402,000); horses (420,000); goat (399,000); red deer (405,000); pigs (375,000) and dogs (390,000). 5. Isoelectric points were estimated: cattle, sheep, goat and red deer (pH 3.5); pig (pH 3.6); dog (pH 3.7) and horse (pH 3.9).
