An ion-suppression reverse phase high pressure liquid chromatographic method is described for the determination of aldicarb, aldicarb sulfoxide, and aldicarb sulfone in potatoes. Samples are extracted with methylene chloride and Na2SO4, evaporated to dryness, and cleaned up using Sep-Pak silica and Sep-Pak-C18 cartridges. The extract can be successfully analyzed by high pressure liquid chromatography on either a mu LiChrosorb RP-18 or mu Bondapak C18 column and quantitated using a variable wavelength ultraviolet detector set at either 220 or 247 nm. The mobile phase is acetonitrile-buffer (4 + 96) and (30 + 70), buffered to pH 7.6 and flowing at 2 mL/min. Recoveries ranged from 80 to 100%. The minimum detectable amount was 37.5 ng, which easily permitted the quantitation of 0.1 ppm aldicarb sulfone in 75 g sample. The recovery of aldicarb was low because of its rapid enzymatic oxidation to aldicarb sulfoxide and sulfone.