The potential invasive Old World bollworm, Helicoverpa armigera (Hübner), widely distributed in the Old World, has not yet been detected in the United States. Helicoverpa species currently are being monitored for possible presence of H. armigera in cotton- (Texas) and corn-growing (Oregon) areas by the use of pheromones. The taxonomic history of Helicoverpa armigera (Hübner) and Helicoverpa zea (Boddie) is discussed. Heliothis stombleri Okumura and Bauer is a new synonym of H. zea. Male genitalic characters that diagnose H. armigera and H. zea are described and illustrated. Methods for examining large samples of H. zea for possible H. armigera specimens are discussed.