The traditional thin-layer chromatography (TLC) is a sensitive technique frequently used in chemical analysis for semiquantitative determinations. In the last years a high-performance thin-layer chromatography system (HPTLC) has been developed. It assures quantitative determinations with direct densitometric measurements of chromatographic spots in situ on the plate. Here, we wish to report a method for the drug determination in street samples, that employs a CAMAG TLC/HPTLC Scanner Photodensitometer and a CAMAG LINOMAT III for sample application. Samples of illicit drug traffic (50 samples of street heroin and 30 samples of street cocaine) are tested and the gas-liquid chromatography (GLC) and HPTLC determinations are compared. The HPTLC method has proven to be sensitive, precise and accurate for quantitative determinations of drugs in street samples. Furthermore this method may be useful in forensic chemistry to show a "fingerprint" of each sample.