A rapid and selective reversed-phase high-performance liquid chromatographic assay with gradient elution and diode-array detection for diacetylmorphine, morphine, codeine, and their free and glucuronidated metabolites in plasma, was developed. After addition of ethylmorphine as internal standard the plasma samples were extracted using C18 ODS-2 solid-phase columns with a recovery better than 80%. The limit of quantitation using an injection volume of 2 microl was 25 ng/ml for each compound. The intra- and inter-day precision was better than 5%. The described method cannot only be used for pharmacokinetic studies but also for intoxication cases to monitor a wide range of opiates.