Contemporary cultivation of field crops utilizes new findings of biotechnologies, specifically recombinant DNA and transgenous techniques to an ever-increasing extent. Transgenic plants enriched in various new genes already became common practice in agriculture of a number of developed but also developing countries. The research in this field intensively grows, also entirely new directions, in addition to already proved gene manipulations, are the subject of interest. The contribution deals with classification and function of some protease inhibitors utilizable in transgenosis of plants. It concentrates also on the aspects associated with possible use of their recombined genes in enhancement of resistance of plants to insect pests and some pathogens. Some examples are given of important transgenic plants which already express genes for most important protease inhibitors.