The 2C, 2C-T, and DO series of designer drugs pose a number of challenges to forensic toxicology laboratories. Although these drugs are seized by law enforcement agencies throughout the United States, they are not readily detected in forensic toxicology laboratories. A systematic evaluation of the cross-reactivity of 9 commercial enzyme-linked immunosorbent assays (ELISAs) was conducted using 11 designer drugs. Cross-reactivity was measured towards 2,5-dimethoxy-4-bromophenethylamine (2C-B), 2,5-dimethoxyphenethylamine (2C-H), 2,5-dimethoxy4-iodophenethylamine (2C-I), 2,5-dimethoxy-4ethylthiophenethylamine (2C-T-2), 2,5-dimethoxy-4isopropylthiophenethylamine (2C-T-4), 2,5-dimethoxy-4propylthiophenethylamine (2C-T-7), 2,5-dimethoxy-4bromoamphetamine (DOB), 2,5-dimethoxy-4-ethylamphetamine (DOET), 2,5-dimethoxy-4-iodoamphetamine (DOI), 2,5-dimethoxy-4-methylamphetamine (DOM), and 4methylthioamphetamine (4-MTA). Cross-reactivity towards the 2C, 2C-T, and DO series of psychedelic amphetamines was < 0.4%. Concentrations as high as 50,000 ng/mL in urine, which greatly exceed those expected in forensic case samples, were not sufficient to produce a positive result. The only substance to produce any measurable cross-reactivity was 4-MTA. Cross-reactivities of 5 and 7% were obtained using four methamphetamine/MDMA directed assays, 25 and 200% using two amphetamine-directed assays. The absence of any measurable cross-reactivity towards the 10 2C, 2C-T, and DO psychedelic phenethylamines makes it harder to detect these drugs using routine screening. As a consequence, laboratories that rely upon immunoassay rather than more broad spectrum chromatographic screening techniques, may fail to detect these powerful psychedelic substances.