Samples that resemble typical case specimens were prepared and shipped to approximately 100 laboratories. Participation varied between 61 and 73%. Tissue samples obtained from laboratory animals can be used to simulate those encountered by forensic toxicologists. This has been demontrated using liver homogenates from animals administered pentobarbital and methaqualone and propoxyphene and acetaminophen. There was a large coefficient of variation however, for the quantitation of acetaminophen in liver. The qualitative data obtained during the course of this study showed a very low incidence of false positives. However, there was a disappointingly low percentage of positive responses for (a) low concentrations of secobarbital and (b) the opiate narcotics (morphine and codeine) in blood, despite the fact that sensitive immunoassay procedures are available for detecting these particular compounds in blood samples. The quantitative determination of drugs and metabolites, other than ethanol, shows wide interlaboratory variation. This variation is presumably not a result of the use of different analytical techniques, since gas liquid chromatography was used by the majority of participants to quantitate drugs and metabolites. Forensic toxicologists are willing to participate in a voluntary proficiency testing program conducted by an independent agency. The performance data developed in this study can serve as a baseline for current forensic toxicology laboratory functional capability in the assessment of future changes and improvements in analytical forensic toxicology. (Author abstract)