The contents of a bottle, from which a human being was reported to have drunk and which were believed responsible to an organophosphorus poisoning, were submitted for chemical analysis. Initial screening by gas chromatography with phosphorus, sulfur and nitrogen specific detectors failed to identify any intact organophosphorus pesticide. Mass spectrometric techniques were applied to the identification. Field ionization, field desorption, chemical ionization, exact mass measurements at high resolution, and GC/low resolution mass spectrometry were used to help define the qualitative and partial quantitative nature of the sample components. Results of this study were consistent with the virtually complete conversion of the pesticide diazinon into a mixture of at least twenty-six chemically distinct products or impurities. The most abundant chemical compounds found in the sample included: 2-isopropyl-4-methyl-6-mercaptopyrimidine (2814-20-2); 2-iso-propyl-4-methyl-6-mercaptopyrimidine; 6,6'-dithiobis-(2-isopropyl-4-methylpyrimidine); 6,6'-thiobis-(2-isopropyl-4-methylpyrimidine); 4-ethoxy-2-isopropyl-6-methylpyrimidine (72799-31-6); 4-thioethoxy-2-isopropyl-6-methylpyrimidine; triethylphosphorothionate and triethylphorothiolate. Also found were several potent acetylcholinesterase inhibiters: monothionotetraethylpyrophosphate; dithionotetraethylpyrophosphate (3689-24-5), tetraethylpyrophosphate. Model decomposition studies verified the formation of these compounds. These results were then used to identify compounds in two other samples.