alpha-Amylases from human urine, pancreas, and saliva were purified to homogeneity. Their molecular and catalytic properties were similar with respect to relative molecular masses, stability, and absorbance in neutral solution, but their isoelectric points differed clearly. Salivary amylase was more sensitive than the other two to inhibition by iodoacetate and EDTA, suggesting a less compact structure. The intermediate qualities of the urinary activity were ascribed to the fact that this enzyme originates from other two without major modifications by metabolism. Human alpha-amylase should be considered as a sole enzyme with multiple forms originating from glycosylation and deamidation. There was no evidence for real isoenzymes.