OBJECTIVES: The purpose of this study is to develop the gas chromatographic-mass spectrometric method (GC-MS) for screening and semiquantification of drugs and drugs of abuse in human serum. METHOD: GC-MS method after liquid-liquid extraction (LLE) and derivatization with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) is presented for screening as well as identification and semiquantification of the most frequently used drugs and drugs of abuse in human serum. RESULTS: Bovine serum spiked with ephedrine (EPHE), 3,4-methylenedioxymethamphetamine (MDMA), guaifenesin (GUAIF), tramadol (TRAM), phenobarbital (PHENO), amitriptyline (AMITR), cocaine (COCA), mirtazapine (MIRTA), dothiepin (DOTH), citalopram (CITAL), clomipramine (CLOMI), bromazepam (BMZPM), diazepam (DZPM), codeine (COD), morphine (MORPH), levomepromazine (LEVO), zolpidem (ZOLP), clozapine (CLOZP), alprazolam (ALPZM) was used for the recovery and repeatability study and for preparation of calibration curves of individual compounds or their TMS derivatives. Recoveries were tested on concentration levels 0.05, 0.1 and 0.5 microg/mL (n=6) and established in range 72.0-98.0%. Repeatabilities expressed as relative standard deviations (RSDs) measured at concentration levels 0.05, 0.1 and 0.5 microg/ mL (n=6) were lower than 10.0%. The calibration curves for analytes or their TMS derivatives were linear in concentration range 0.025-2.000 microg/mL (except of EPHE 2TMS, MDMA TMS, MORPH 2TMS, BMZPM TMS, ALPZM) with correlation coefficients exceeding 0.99. The limit of quantification (LOQ) for analytes used for evaluation study was 0.025 microg/mL (except analytes mentioned above). CONCLUSIONS: The GC-MS method presented here is allowing screening, identification and semiquantification of the most commonly encountered drugs and drugs of abuse in human serum and can be successfully applied to analysis of real samples from clinical and forensic toxicology cases.