Perchlorate is an emerging contaminant associated with military and defense-related activities that has been detected in a variety of products ranging from food and water to vitamins. Because of its potential to interfere with normal thyroid functioning in humans, exposure from food products is a major concern. We have previously shown using hydroponic experiments that low part-per-billion levels of perchlorate—similar to those found in the Colorado River—accumulate in lettuce leaves, and the extent of accumulation varies with lettuce type. To fully understand the key factors controlling perchlorate uptake in higher plants, we have extended our studies to examine the competitive role of soil anions on perchlorate accumulation in crisphead, butter head, and green leaf lettuce. Separate experiments were conducted in which the effects of nitrate, sulfate, chloride, or bicarbonate on perchlorate accumulation were tested. Lettuce was grown in hydroponic solution containing 5 mg/L perchlorate and varying concentrations of the tested anions. Increasing sulfate concentrations from 1 to 10 mM had no effect on perchlorate accumulation. Increasing bicarbonate concentrations from 2 to 5 mM and increasing chloride concentrations from 5 to 15 mM both marginally decreased perchlorate accumulation in all three genotypes; however, in most cases these effects were not statistically significant. Nitrate had the most dramatic effect on perchlorate accumulation: increasing nitrate concentrations from 4 to 12 mM significantly decreased perchlorate accumulation in crisphead (56%), butter head (49%), and green leaf (53%) lettuce. The data support the notion that perchlorate may enter higher plants via nitrate-specific membrane transporters.