The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is an invasive pest of soybean [Glycine max (L.) Merr.]. Since the first report in the United States in 2000 it has become one of the most damaging soybean pests. Three soybean aphid biotypes have been reported to date. The objective of this research was to determine whether an A. glycines field isolate collected near Lomira, WI, was unique from those previously reported. The response of the Lomira isolate was compared to existing soybean aphid Biotypes 1, 2, and 3 by conducting caged and noncaged assays using 10 soybean genotypes. In both the caged and noncaged assays, there were significant effects (P < 0.0001) of soybean aphid isolate, genotype, and soybean aphid isolate × genotype interaction. The Lomira isolate reaction profile was different than those of previously reported biotypes, therefore identifying a new biotype to use in characterization of soybean aphid resistant germplasm.