A simple method has been developed for the measurement of mexiletine and lignocaine in blood-plasma or serum at the concentrations attained during therapy. A relatively small (200 microliter) sample volume is made basic and extracted with 50 microliter of chloroform containing internal standards, and the extract is analysed directly by gas-liquid chromatography with flame-ionisation detection on two separate columns. The instrument calibrations are linear and pass through the origin of the graphs. Neither solvent transfer nor evaporation steps are used in the extraction procedure, which takes less than 3 min to complete, and no interference from either endogenous sample constituents or other drugs has been observed.