Basic drugs were extracted from 1 mL of serum, urine, or other biological fluids under alkaline conditions into hexane:isoamyl alcohol (98:2). The drugs were back-extracted into acid and re-extracted into 50 microL of chloroform:isoamyl alcohol (95:5) after the acid had been alkalinized. An aliquot of the chloroform:isoamyl alcohol was injected onto a temperature programmed gas chromatograph equipped with two nitrogen phosphorus detectors and two fused silica capillary columns fitted into a single injector. Results obtained from 388 serum samples (from suspected overdose patients) tested using this procedure are presented. The same extraction applied to a variety of body fluids proved reliable for quantitations of several of the basic drugs when a packed column was used.