A fatality following ingestion of diazepam and 4,5-dihydro-4-methyl-5-phenyl-2-oxazolamine, a cyclic derivative of phenylpropanolamine known as U4EuH or 4-methyl aminorex, is described. Solid dosage samples of U4EuH were analyzed using gas chromatography, ultraviolet and infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry. Physiological fluids were analyzed quantitatively by gas chromatography and qualitatively by gas chromatography-mass spectrometry. Concentrations of 4,5-dihydro-4-methyl-5-phenyl-2-oxazolamine were: in blood 21.3 mg/L; in urine 12.3 mg/L. Diazepam concentration in blood was 0.8 mg/L.