The unknown material with an Rf value of about 0.30 in a TLC system consisting of cyclohexane/toluene/diethylamine (75:15:10 volume/volume) was isolated from the silica gel plate after spraying with Dragendorff reagent. Five isolations of the unknown material and its chromatographic behavior were checked in both a basic solvent system as well as a neutral solvent system (chloroform/methanol 90:10 v/v) as typically used for cocaine identification. Ultraviolet spectra showed typical benzenoid absorptions which indicated the presence of a benzenoid moiety in the molecule; exposure to gas chromatography yielded breakdown products due to thermal degradation. A direct probe mass spectrum identified one or more truxilline isomers on the basis of the fragmentation pattern. This is the first time isomeric truxillines were isolated and identified in illicit cocaine using TLC methodology. Their presence may indicate the natural origin of the cocaine. Using TLC with solvent system B followed by spraying with Dargendorff, reagent truxillines can be confirmed in illicit cocaine samples. 1 table, 13 figures, and 18 references (Author abstract modified)