By means of thin-layer chromatography, an unidentified alkaloidal fraction was observed in illicit cocaine. Because of its persisting presence, efforts were undertaken to isolate and identify this fraction. Various analytical techniques showed complex results, finally pointing to the possibility of isomerization of constituents of the fraction. A direct-probe mass spectrum showed a fragmentation pattern which could only fit a truxilline. When using thin-layer chromatography, at least five isomers could be observed. This is the first time truxillines have been observed, isolated, and identified by thin-layer chromatography.