The Center for Human Toxicology has, together with other toxicology laboratories, been involved in the field evaluation of a radioimmunoassay procedure for the detection and quantitation of delta 9-THC in serum and an enzyme multiplied immunoassay procedure for the detection of the nor-carboxylic acid metabolite in urine. Each laboratory was selected on the basis of proven experience with commercially available immunoassay procedures. Initially, the study was designed to screen samples collected from accident casualties; however, at some of the study sites the data base was extended to include other samples. The radioimmunoassay procedure evaluated was developed at the Receptor Research Institute, and involves the use of a tritium-labeled delta 8-THC tracer. A total of eight laboratories participated in the evaluation of this method, which is prepared in kit form by the manufacturer. Thirteen laboratories evaluated the EMIT procedure developed at Syva Corporation. The study protocol required that each site screen serum and urine samples and forward all presumptive positive specimens to the Center for Human Toxicology. These positive specimens were then shipped to either Battelle Laboratories or Research Triangle Institute for confirmation analysis by gas chromatography-mass spectrometry. The results of these evaluations will be presented and will include: 1. Correlations of positive RIA and EMIT analysis with gas chromatography-mass spectrometry results; 2. The results of quality-control tests; 3. Criticisms and suggestions made by analysts at each site; 4. The results of evaluations performed at the Center for Human Toxicology.