We have identified morphine and codeine in human urine by means of gas chromatography/mass spectrometry. Gas chromatography/mass spectrometry was also used to quantitate the two alkaloids and tetrahydropapaveroline (THP) in urine of both normal subjects and parkinsonian subjects receiving L-dopa therapy. The morphine, codeine and THP levels in healthy nondrinker controls were 2.93 +/- 0.23, 2.01 +/- 0.53 and 6.70 +/- 1.13 pmol/ml (mean +/- S.E.M.), respectively. In contrast, the urinary levels of codeine and THP in L-dopa-treated parkinsonian patients were significantly elevated to 62.20 +/- 17.54 and 31.04 +/- 15.69 pmol/ml, respectively. Some of the parkinsonian patients showed high urinary morphine levels. Morphine excretion was also enhanced in patients complaining of severe pain due to herpes zoster (24.60 +/- 9.51 pmol/ml) but not in patients with severe pain due to cerebral embolus. These alkaloid levels in the urine of abstinent alcoholics were very low. There were significant correlations among these three alkaloid levels in the urine. The results indicate that morphine and codeine are synthesized in the body from L-dopa and/or dopamine, via the THP-related pathway.