Bt cotton has been planted to the exclusion of non-Bt cotton in the Yellow River cotton-farming region of China since 2000. Alternative non-Bt hosts, such as maize, soybean, peanut, wheat, and other host plants of Helicoverpa armigera (Hübner) may be acting as refuges for Bt-susceptible larvae of this pest, thereby delaying evolution of resistance to Bt cotton. Egg, larval, and adult densities of H. armigera were measured on Bt cotton, and on maize that was planted on dates that reflected local farming practices, in order to assess the role of maize as a refuge during 2001?2002 in Xinxiang County, Henan Province and Anci County, Hebei Province. The results indicated that the average egg densities for the second?fourth generation of the pest on Bt cotton in Xinxiang and the second generation in Anci County were significantly higher than those in maize fields. However, maize typically had much higher larval densities in the third and fourth generation of H. armigera than on Bt cotton. These data indicate that maize is probably serving as an effective refuge for third and fourth generation H. armigera, but is of less value for the second generation. The densities of moths produced by Bt cotton and by maize in a cage experiment confirmed the importance of maize as a refuge in the third and fourth generation.