Results of 3-years investigations on changes in the activity of nitrate reductase and the content of nitrates, water soluble sugars, and starch in leaves of plants of two pea cultivars treated with Ambusz 25 EC (permetrin) and Ripcord 40 EC (cypermetrin) were presented. It was found that the applied insecticides brought about the greatest changes in the activity or nitrate reductase and in the content of nitrates. Of the two cultivars investigated Beniaminek manifested a stranger susceptibility to the applied insecticides. Side effects of pyretroids depend on the stages of plant development, the greatest effect being observed at the stage of technological maturity of pea seeds.