A technique was studied and later implemented to determine the amount of polyphenoloxidase removable from soils. This enzymatic activity favors oxidation processes such as those of phenols. These are the foundations for the synthesis of highly stable polymers, such as soil humus. A prospection of polyphenoloxidase activity was performed in seven volcanic soils, with high content of stabilized organic matter, humus type, and in two alluvial soils, of low content of organic matter. The polyphenoloxidase activity was greater in volcanic than in alluvial soils. Besides, such activity underwent periodical variations of relative importance in some soils. Storaye and changes in soil moisture depressed polyphenoloxidase activity.