Studies were conducted at East Lansing, MI, in 1994 and 1995 to examine corn yield response to giant foxtail interference and to examine the effect of giant foxtail density on giant foxtail biomass, seed production, and seed germination. Treatments consisted of 0, 10, 30, 60, 84, and 98 giant foxtail plants m−1 of row in 1994 and 0, 10, 27, 30, 60, and 69 plants m−1 of row in 1995. The influence of giant foxtail density on corn yield fit a hyperbolic equation. Corn yields were reduced 13% in 1994 and 14% in 1995 from 10 giant foxtail plants m−1 of row. Corn dry matter at maturity was decreased 24 and 23% from 10 giant foxtail plants m−1 of row in 1994 and 1995, respectively. Giant foxtail seed production increased linearly as inflorescence length increased. The length of a single giant foxtail inflorescence increased as plant density increased and the number of inflorescence produced per plant decreased. Giant foxtail seed production ranged from 518 to 2,544 seeds per plant. Ten giant foxtail plants m−1 of row produced 15,700 seeds m−2. Giant foxtail seed germination was not affected by plant density.