A stable isotope dilution LC-MS/MS method was developed for the Alternaria toxins alternariol (AOH), alternariol monomethylether (AME) and tenuazonic acid (TeA) in herbs. Tentoxin (TEN) was quantified using matrix calibration. Solid phase extraction was applied for sample purification. Limits of detection (LOD) and quantification (LOQ), recoveries and intra- and interday precisions were determined for a comprehensive validation. The method was used to evaluate the mycotoxin contamination in various herbs and infusions.