Season-long interference of shattercane, giant foxtail, common cocklebur, and common lambsquarters in corn was evaluated in the field at weed densities from 0.4 to 13.1 plants or clumps/m of corn row during 1985, 1986, and 1987. Corn seed yields decreased linearly with increases in the density of clumps of 2 to 3 shattercane plants and 5 to 8 giant foxtail plants, reaching 22% yield loss at 6.6 shattercane clumps/m of row and 18% yield loss at 13.1 giant foxtail clumps/m of row. Increases in common cocklebur density caused corn yields to decrease curvilinearly in 1985 with a maximum predicted yield loss of 27% occurring at a density of 4.7 common cocklebur plants/m of row. In 1986 and 1987, yields decreased linearly as common cocklebur density increased to 6.6 plants/m of row, where a 10% yield loss was observed. Common lambsquarters reduced corn yields only in 1985. In this year, yields decreased curvilinearly with increasing weed density, resulting in a maximum yield loss of 12% at 4.9 common lambsquarters plants/m of row. Corn yields averaged 11600 kg/ha when grown without weed interference in these experiments.