Changes in the peptide hydrolase isoenzymes of wheat tissues in different ontogenic status were followed throughout the differentiation and the dedifferentiation processes. After electrophoresis of tissue extracts, zymograms were obtained with different chromogenic substrates inorder to identify distinct types of esterase and amidase activities. The variations observed in the isoenzymes of the different tissues clearly reflected modifications occurring at the various stages of their development. A highly differentiated tissue, as the endosperm, expresses a restricted number of peptide hydrolase activities. Conversely, an undifferentiated tissue (callus), originates a very complex zymogram which shows the least repressed genetic capacity of this tissue.