Three formulations of 2,4-D were tested in rats for their ability to increase landing foot splay, a measure of ataxia. When administered for three to four consecutive days, 2,4-D-n-butyl ester (150 mg/kg/day SC) produced significant increases in landing foot splay while 2,4-D acid (120 mg/kg/day SC) and 2,4-D mixed butyl esters (150 mg/kg/day SC) did not. The ability of acute n-butanol, 2-butanol, and a 50:50 mixture of both (2.13 mM/kg SC) to increase landing foot splay was then assessed. Only n-butanol significantly increased landing foot splay. Similarly, when n-butanol was administered daily, at doses corresponding to 150 mg/kg/day of the 2,4-D-n-butyl ester, significant increases in landing foot splay were evident. The pattern of splay increases was remarkably similar to that observed for 2,4-D-n-butyl ester. When locomotor activity was the dependent variable, daily n-butanol had no effect. These results suggest that in vivo formation of n-butanol after administration of 2,4-D-n-butyl ester is responsible for the motor incoordination but not the depression of locomotor activity observed following 2,4-D-n-butyl ester administration. These data demonstrate that different formulations of the same herbicide can produce differential behavioral effects.