Xylenes have the potential for widespread public exposure, yet their neurotoxic properties are poorly understood. The conditioned flavor aversion (CFA) paradigm provides a sensitive behavioral assay for the aversiveness of many drugs and toxic chemicals. Male Long-Evans rats were placed on a restricted water schedule (30 min/day) 1 week after arrival in the laboratory at 40 days of age. Ten days later, all rats received 0.2% saccharin in place of water, and then were exposed immediately either to conditioned air or to 50, 100, 200, 400, 800 or 1600 ppm p-xylene for 4 hr, or to 400 ppm p-xylene for 0.5, 1, 2, 4, or 8 hr. The restricted water schedule remained in effect for the next 72 hr, at which time the rats were given a choice between saccharin and water. Inhalation of all concentrations of p-xylene reduced preference for saccharin, with maximal aversion at 800 and 1600 ppm. The aversion produced by p-xylene was maximal at exposures of 2 or more hrs, with shorter exposures producing intermediate effects. Thus inhaled p-xylene at a concentration of 1/2 its TLV (100 ppm) caused a significant, learned change in rats' normal flavor preference for saccharin without disrupting fluid consumption.