A method using gas chromatography coupled to mass spectrometry for the determination of cocaine (COC) pyrolysis product, anhydroecgonine methylester (AEME), in plasma, saliva, urine, sweat and hair is described. The same procedure allows the simultaneous determination of COC, benzoylecgonine (BZE), ecgonine methylester (EME) and cocaethylene (CE). After suitable sample preparation (desorption of the sweat patch, acid hydrolysis of the hair) the target drugs were extracted using a 3-steps liquid-liquid extraction (pH 8.4) in presence of deuterated internal standards in chloroform-isopropanol-n-heptane (50 : 17 : 33, v/v). Derivatization was achieved using BSTFA+1% TMCS. Ions for AEME monitoring were m/z 82, 166, 152 and 181. Artifact formation from COC or EME of AEME during the injection was less than 0.5%. AEME was never detected in blood sample although the corresponding urine tested positive. Urine concentrations, in about 90 positive AEME samples, were in the range 5 to 1477 ng/ml. In one case of crack overdose, AEME in sweat was 53 ng/patch with a COC concentration of 1231 ng/patch. AEME in saliva ranged from 5 to 18 ng/ml in the same case. Finally, AEME was identified in 32 hair specimens of crack abusers including fetal hair, with concentrations in the range 0.20 to 21.56 ng/mg. These results suggest that AEME can be a useful marker for the detection of COC smoking in clinical and forensic cases.