Competitive effects of cocklebur (Xanthium pensylvanicum Wallr.) and redroot pigweed (Amaranthus retroflexus L.) on cotton (Gossypium hirsutum L.) were evaluated in four experiments at two locations in Alabama during the period 1966 to 1968. Cocklebur was more competitive with cotton than was pigweed on Norfolk sandy loam soil. A density of eight cocklebur plants per 7.31 m of row reduced cotton yields 20 to 40%. Higher densities of cocklebur resulted in greater yield reductions. Forty-eight cocklebur plants per 7.31 m of row caused cotton yields to be reduced more than 80%. Pigweed at a density of 48 weeds per 7.31 m of row reduced cotton yields less than 50% on the Norfolk soil. On Lucedale sandy clay loam, cocklebur and pigweed were equally competitive and both species were more competitive than on Norfolk soil. A density of eight cocklebur or pigweed plants per 7.31 m of row resulted in 60 to 70% cotton yield reductions. The highest density of pigweed studied, 48 plants per 7.31 m of row, reduced cotton yields 90% on the Lucedale soil. Vegetative growth, boll, and seed size were not affected as much as cotton yields by either weed species. Percentage lint and fiber properties were unaffected by plant competition.