Field experiments were conducted at Stuttgart, AR, from 1986 to 1988 to determine effects of season-long interference of red rice densities of 1, 2, 5, 10, 20, and 40 plants m–2 on ‘Lemont’ and ‘Newbonnet’ rice cultivars. This interference reduced straw dry weights of Newbonnet and Lemont by 100 and 130 kg ha–1 per red rice plant, and grain yields by 178 and 272 kg ha–1 per red rice plant, respectively. Grain yield reductions were due to decreases in panicle number and length, and in number of grains per panicle. Ten plants m–2 or more reduced height of Lemont, while 40 plants m−2 were required to reduce height of Newbonnet. Red rice at 10 plants m−2 or more reduced total milled and head rice yields of Lemont, but red rice did not affect these components for Newbonnet. Red rice interfered with rice, even at densities as low as two plants m−2, and interference was greater in Lemont, a semidwarf cultivar with mature plants 92 cm tall, than in Newbonnet, a conventional cultivar with mature plants 115 cm tall. Red rice produced more panicles m−2 and 31 to 64% greater straw dry weight when grown with Lemont than when grown with Newbonnet because red rice shaded Lemont more than Newbonnet. Red rice plants grew taller as red rice densities increased and also were taller when grown in Newbonnet than when grown in Lemont.