A simple GLC procedure for the detection and quanti-tation of possible impurities in levodopa raw material and commercial dosage forms is presented. The sample is reacted with N,O-bis(trimethylsilyl)acetamide in acetonitrile at ambient temperature for 30 min, and the silyl derivatives are separated on a methyl silicone column under isothermal conditions. Peak areas are measured using an electronic digital integrator of wide input signal range capacity. The results obtained by applying the procedure to the analysis of several multicomponent simulated mixtures were in good agreement with theoretical values. Only 3-methoxy-4-hydroxyphenylalanine was detected as a contaminant in each of the five commercial products examined.