A gas chromatographic-mass spectrometric assay for eight opium alkaloids in human urine following opium ingestion is described. The compounds were extracted from urine with methylene chloride-isopropanol (7:3, v/v) at pH 9.5, evaporated, derivatized with Tri-Sil Z and analyzed by methane chemical ionization mass fragmentography. The method in sensitive to ca. 0.01 microgram/ml for morphine and codeine and ca. 0.05 microgram/ml for the other compounds. Adsorption problems on the gas chromatography column prevented obtaining reproducible results for the measurement of noscapine. Extraction efficiencies over the pH range of 8-11 for the eight compounds are reported. Retention times of the opium alkaloids were determined using five different liquid phases (3%) on Gas-Chrom Q (100-120 mesh) and two column lengths (36 cm and 183 cm). The 36-cm column packed with OV-210 was selected for use in the assay. Ions were selected for monitoring for each component from their methane chemical ionization spectrum to provide the needed sensitivity and specificity for analysis of a multi-component mixture. The assay was used for the analysis of an "opium eater's" urine. Morphine, codeine, nomorphine, norcodeine and noscapine were detected; however, no evidence was obtained for thebaine, papaverine or oripavine. Unconjugated morphine (0.64 microgram/ml) was present at nearly twice the concentration of codeine (0.37 microgram/ml) and normorphine and norcodeine were present in equal amounts (ca. 0.15 microgram/ml).