A liquid chromatographic method with UV detection was developed for the separation and quantification of six amphetamines in the presence of adulterants in illicit drugs. Comparison was made between a regular reversed-phase and a base-deactivated column. The mobile phase composition was optimized by studying the influence of pH, buffer composition and the organic solvent type. Validation was accomplished by examination of the linearity, precision, accuracy, limits of detection and limits of quantification of the method. Amphetamines were quantified in eight tablets obtained from illicit drug seizures and the results were verified by a GC-MS procedure.