CHEMICAL ANALYSES OF ILLICIT DRUGS SERVE TWO MAIN PURPOSES. THEY FORM THE LEGAL PROOF FOR CONVICTION OF NARCOTICS PEDDLERS AND ARE USED AS INSTRUMENTS FOR THE PERFECTION OF POLICE INTELLIGENCE WORK. TO AID THE POLICE, THE DETAILED RESULTS OF ANALYSES CONDUCTED BY THE NATIONAL LABORATORY OF FORENSIC SCIENCE OF SWEDEN ARE GENERALLY TRANSMITTED TO THE POLICE IN A WRITTEN REPORT AND IN A COMPUTER INPUT SHEET, SENT IN CODED FORM. CHEMICAL COMPOSITION ALONE, FED INTO THE CENTRAL POLICE COMPUTER SYSTEM, ALLOWS CERTAIN CONCLUSIONS TO BE DRAWN. WHEN DRUGS SEIZED AT DIFFERENT LOCATIONS THROUGHOUT THE COUNTRY HAVE SIMILAR COMPOSITIONS, A COMMON SOURCE MAY BE INDICATED. SPECIAL ANALYSIS ACTIVITY THUS INVOLVES TWO MAIN ASPECTS: THE DIRECT COMPARISON OF THE CHEMICAL SIGNATURES AND THE POSSIBLE EVALUATION OF THE SYNTHESIZING METHOD USED FOR CLANDESTINELY PREPARED NARCOTICS. OBTAINING DIFFERENT TYPES OF SIGNATURES ENHANCES THE POSSIBILITY OF ESTABLISHING A COMMON ORIGIN OF DIFFERENT SAMPLES. KEY IMPURITIES ARE OF GREAT INTEREST IN THE FORENSIC ANALYSIS OF NARCOTICS. THEIR RECOGNITION AMONG THE NUMEROUS GAS CHROMATOGRAPHIC PEAKS WHICH CONSTITUTE THE CHEMICAL SIGNATURE SHOULD THEREFORE BE AN IMPORTANT QUESTION FOR FORENSIC LABORATORIES. THE 'CLASSICAL' METHOD FOR RECOGNITION OF AN ORGANIC COMPOUND MIXTURE IS GAS CHROMATOGRAPHY-MASS SPECTROMETRY. IMPURITIES MAY ALSO BE IDENTIFIED THROUGH LESS SOPHISTICATED METHODS. A GAS CHROMATOGRAPH WITH A DUAL DETECTOR SYSTEM SHOULD HAVE SUFFICIENT DISCRIMINATION POWER. FIGURES AND REFERENCES ARE INCLUDED. (LWM)