The underlying principles of the commonly used radioimmunoassay, enzyme immunoassay, fluorescence polarization immunoassay, and particle, immunoassay are outlined. Cross-reacting characteristics of these immunoassays as reported by the manufacturers and independent laboratories are talmlated. These information show that commercial imnninoassay kits for drug categories that are included in workplace drug urinalysis programs are generally more specific than those kits that are for dinical uses only. Furthermore, recently manufactured immunoassay kits targeted for use in workplace drug urinalysis programs are more specific than those manufactured earlier. Reported effects of adulterants, such as salt^ cleaning agents. etc., on commonly used immunoassays are summarized. Without more comprehensive and systematic studies, it is difficult to make general statements concerning the superiority of one methodology over the others. It is dear, however, that cannabinoid assays are most susceptible to the influence of adulterants.