The soybean aphid Aphis glycines Matsumura, a serious pest of soybean in China, was first detected in the U.S. on 13 July 2000 in a research trial conducted by the authors on a private farm near Whitewater, WI. Although the aphids we collected appeared to be the cotton/melon aphid, an aphid already present in the U.S., we forwarded specimens to Dr. David Voegtlin at the Illinois Natural History Survey for additional examination. Dr. Voegtlin determined that the aphids were soybean aphid; the cotton/melon aphid and the soybean aphid closely resemble one another and separation of the of the identities of the two species is difficult. The cotton/melon aphid, Aphis gossypii, is reported to colonize on soybean in China. And there also are reports that the two species can hybridize when the overwinter on the same plant. By the fall of 2000, the presence of soybean aphid had been confirmed in nine states, but it appears that the heaviest infestations were present in Wisconsin, Michigan, and northern Illinois.