Peptidases have several applications in food processing and biotechnology, such as bakery, meat tenderizing, cheese maturation, wastewater treatment, production of protein hydrolysates, etc. They account for 60% of the enzyme market. Some plants immediately secrete latex when the leaves and stems are injured. Latex itself may act to shield the cambial meristem and the contents of the sieve tubes from predators, or to ward off parasites or pathogens. Therefore, it seems reasonable to assume that the substances and enzymes needed for such purposes are present in latex.A significant number of research projects aim to screen new peptidase sources that could be applied for biotechnological purposes. Preliminary data showed that the latex from E. milii possess an active serine peptidase, and accordingly, the present work intended to immobilize that peptidase. Immobilized enzymes have been defined as those physically contained, maintaining its catalytic activity, and suitable for continuous utilization. In order to reach that objective, we had to standardize the immobilization method, as well as the tests and stability protocols. We collected latex samples obtained by cutting the stem. Latex was mixed with acetate buffer (pH 5,0; 50mM) and subsequently processed for two different immobilization approaches: using Polyacrylamide and by lyophillization. The proteolytic activity was measured by 1% casein hydrolysis at 37^oC, being proportional to the abrorbance increase at 280nm. The enzyme immobilized by lyophillization lost its activity after 7 days. For polyacrylamide we adopted a protocol after trying several variations. The gel was prepared using, besides the usual ingredients, Tris buffered solution pH 8.0, containing EDTA 0,1 mM and b-mercaptoethanol. The gel was cut in small cubes of about 3mm and washed, to release the unrestrained enzyme. Proteolytic activity of the immobilized enzyme kept under refrigeration at 4^oC decreased 22% in a 3 months period, being verified by alternate methods such as peptide analysis by SDS-PAGE and the gel diffusion method. Financial Support: FAPESP (03/00085-4) AND CNPq (GOBR) CNPq/ PIBIC (LPM).