The analysis of seeds from yopo (Anadenanthera peregrina) by GC/IRD and GC/MS is presented. The GC/IRD technique is easily able to discriminate between bufotenine (present in yopo seeds) and its positional isomer psilocin. KEYWORDS: Yopo, Anadenanthera Peregrina, Bufonenine, Psilocin, Tryptamines, GC/IRD, GC/MS, Forensic Chemistry