Human pancreatic juice collected antiseptically and strietly free from other body fluids and juices, was examined for the isozyme composition of α-amylase. Unlike those of the extract of and exudate from pancreatic tissue, the composition of α-amylase isozyme in the secreted juice was simple and consisted of only two isozymes, a major one and a minor one, and the reason for the difference in the isozyme composition is discussed. The major α-amylase isozyme was obtained in a crystalline state with a molecular weight of 5.4-5.5 ×104.