The performances of a number of liquid--solid systems, consisting of mixtures of water and methanol as liquid phase and methyl silica as solid phase, were investigated with respect to their use in the separation of barbiturates by high-pressure liquid chromatography (HPLC). Phase system selectivities and column efficiencies were determined. The results were applied to the development of a rapid method for the determination of trace amounts of barbiturates in blood. The first step in the analysis, the extraction of barbiturates from blood, was also investigated and good recoveries were achieved. The extracts were analyzed by HPLC using ultraviolet detection at 220 nm. A low detection limit and high precision were obtained; An amount of 5 ng hexobarbital, for example, can be determined with a precision of +/-15% and 5 mug with a precision of +/-0.3%. The time course of the concentration of hexobarbital in the serum and saliva of man after an oral administration of 400 mg is demonstrated.