This chapter presents the results obtained using homogeneous enzyme-immunoassay for the measurement of cannabinoids in urine and in saliva. Vinson et al. have described a Thin Layer Chromatography (TLC) method for measuring tetrahydrocannabinol (Δ'-THC) in extracted serum or blood. This method utilizes a reagent which forms a fluorescent derivative with phenols. Several groups of investigators have been developing methods which utilize Gas Chromatography (GC) or High Pressure Liquid Chromatography (HPLC) to separate cannabinoids from other components in serum and from each other, in order to quantitate them. The antibodies were elicited in sheep using a bovine-serum albumin conjugate of an aldehyde derivative of Δ'-THC. The antibodies generated for use in this assay were intended to permit detection of various Δ'-THC congeners and metabolites. To monitor the presence or absence of a drug in urine, it is necessary to select a specific minimum "cutoff" level above which samples will be identified as positive.