A method is described to prepare routinely high resolution support-coated open tubular (SCOT) columns. A siliceous support material (Cab-O-Sil) is deactivated with benzyltriphenylphosphonium chloride and deposited on the inside wall of a glass capillary column. After additional coating with a polar stationary phase (OV-225) a number of anticonvulsant drugs can be analyzed without prior derivatization. The columns described show high plate numbers and do not deteriorate in use. The repeatability of the gas chromatographic analysis is better than 1.2% (Orel). The minimum detectable quantity is of the order of 10(-10) g. An improved procedure for isolating the drugs from serum is given, which results in an extraction recovery of better than 90% for the drugs of interest.