These laboratories most commonly produced methamphetamines, phencyclidine (PCP), lysergic acid diethylamide (LSD), amphetamine, and methaqualone. Special techniques are used to determine whether a seized drug has been clandestinely manufactured and to identify its source. These techniques involve detailed physical and chemical examinations. The results of these examinations are computerized and compared with reference samples to provide indications of the drug source. Undercover techniques are also effectively used for the detection of clandestine laboratories. Findings have also shown that the chemicals necessary for the illegal production of drugs of abuse were often diverted from legitimate sources through international commerce, which, together with clandestine laboratories, are recognized as an international problem requiring monitoring through international cooperation. (Author abstract modified)