A high pressure liquid chromatography-diode array detector (HPLC-DAD) method using amylose tris(3,5-dimethylphenyl carbamate) chiral stationary phase (Chiralpak AD-H) is described for the determination of doxylamine enantiomers in human plasma. Doxylamine enantiomers were separated on a Chiralpak AD-H column using a mobile phase composed of n-hexane-2-propanol-diethylamine (98:2:0.025, v/v/v). Diphenhydramine was used as an internal Standard (IS). Doxylamine was extracted from plasma samples using dichloromethane:hexane (1:2v/v), which yielded high extraction yields (87%), satisfactory precision (RSD1.05%), and good selectivity. Linearity was found in the 8-40 mu g center dot mL-1 range with the limits of detection 0.13 mu g center dot mL-1. Doxylamine enantiomers were well separated with no interference from endogenous plasma constituents. The method developed, showed a good linearity, sensitivity, and repeatability.