A capillary column gas chromatographic method is described for the simultaneous determination of morphine, codeine, heroin, 3- and 6-monoacetylmorphine, nalorphine, naloxone, ethylmorphine, and naltrexone. The drugs were extracted from 2 ml plasma, urine, or other biological samples, including tissue under alkaline conditions in chloroform-isopropanol-n-heptane (50:17:33, v/v), with levallorphan as an internal standard. The drugs were extracted into acid and then reextracted into chloroform after the acid had been alkalinized. After derivatization with trifluoroacetic anhydride, an aliquot was injected into a 25m capillary column equipped with a nitrogen phosphorus detector. The lower limits of detectability, extraction recovery, and the within-run and day-to-day precision of results were determined for each drug. Our results indicate that the procedure is suitable for use in overdose screening and therapeutic drug monitoring.