A field study was made on the competitive effect of quackgrass (Agropyron repens (L.) Beauv.) on corn for the nutrients N, P, and K during 1962 and 1963. Quackgrass competition drastically reduced corn height and yield and delayed maturity. High levels of fertilization did not overcome the effects of quackgrass competition. The annual uptake by quackgrass during the growing seasons of 1962 and 1963 was 105, 15 and 60 lb/A of N, P, and K, respectively. Quackgrass shoots harvested at maturity in mid-July had taken up 55, 45, and 68% of the total N, P, and K, respectively, that was removed throughout the season by quackgrass shoots plus rhizomes. It appeared that the early season uptake of N and K by quackgrass may have contributed to, but was not solely responsible for, the reduction in corn height and yield and delayed maturity noted later in the season.