The soybean aphid (Aphis glycines Matsumura) has over the past five years become one of the most important pests of soybean [Glycine max (L.) Merr.]. Four soybean plant introductions (PIs): PI 567598B, PI 567541B, PI 567543C and PI 567597C were found to possess resistance to the soybean aphid in an earlier study. Plants with resistance can negatively interfere with the growth of aphid colonies and can control the insect effectively. Information on the number of major genes controlling resistance to soybean aphids is essential to design efficient breeding schemes to develop soybean varieties with resistance to the insect. The objectives of this study were to determine the number of major genes that underlie the antibiotic resistance to soybean aphids in the resistant PI567598B using F2 and F3 populations. Phenotypic data was used to determine the number of major genes involved in antibiotic resistance.