A liquid chromatography-tandem mass spectrometric (LC-MS-MS) method with a rapid and simple sample preparation was developed and validated for the simultaneous determination of the local anesthetics bupivacaine, mepivacaine, prilocaine and ropivacaine in human serum. An external calibration was used. The mass spectrometer was operated in the multiple reaction monitoring mode. A good quadratic response over the range of 1.0-200.0 ng/ml was demonstrated. The accuracy for bupivacaine ranged from 93.2 to 105.7%, for mepivacaine from 96.2 to 104.3%, for prilocaine from 94.6 to 105.7% and for ropivacaine from 94.3 to 104.0%, respectively. The limit of quantification was 1.0 ng/ml for all substances. This method is suitable for pharmacokinetic studies.