A high-pressure liquid chromatographic method is presented for determining lidocaine and its dealkylated metabolites, monoethylglycinexylidide and glycinexylidide, in plasma. This method uses 20-microliter samples injected directly through a pre-column onto a C18 analytical column. It is fast, sensitive and linear over a concentration range of 1--10 microgram/ml. Since the method requires no preliminary treatment of the plasma, it provides a practical means of monitoring lidocaine and its metabolites in therapeutic situations.