Letosteine has been found to be effective in treating patients with chronic bronchopneumopathies in clinical practice. To provide robust support for its pharmacokinetic and clinical studies, a rapid and sensitive method based on liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was developed and validated for the analysis of letosteine in plasma samples. After protein precipitation, the plasma samples were separated on a reversed-phase C-18 column in less than 1.5 min. The LC-MS/MS system was performed in the positive ion multiple-reaction-monitoring (MRM) mode to produce intensive product ions of miz 280.1 -> 160.0 for letosteine and m/z 248.1 -> 121.1 for the internal standard, tinidazole. The method was found to have excellent linearity (r >= 0.9974), precision (RSD <= 5.83%), extraction recovery (71.8-73.0%) and stability (RE, -8.45% to 9.03%) over a concentration range of 0.1140-152.0 mu g L-1. Compared to the previous published radioactive method, LC-MS/MS method showed many advantages including shorter analysis time, simpler preparation procedure, increased sensitivity as well as lower safety risks. In addition, this method was successfully applied to study the pharmacokinetics of letosteine following a single and multiple dose oral administration in Chinese healthy volunteers. (C) 2011 Elsevier B.V. All rights reserved.