A sensitive high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of ibandronate in human plasma. In a previous study, we have analyzed alendronate in urine samples of subjects treated at therapeutic dosages, using a derivatization approach; a similar derivatization was adapted and improved to determine ibandronate in plasma. The bisphosphonate was isolated from the biological matrix by liquid-liquid extraction, and derivatized with trimethylsilyldiazomethane prior to separation on a reversed-phase column (Supelco Discovery HSC18) and detection on a quadrupole-linear ion trap mass spectrometer (API 4000 QTrap). Various parameters of extraction and derivatization were optimized in order to get adequate recovery, high derivatization yield and minimal ion suppression; a deuterated analogue, d3-ibandronate, was used as internal standard. The transitions 376.1-->114.2 and 379.1-->61.0 were acquired to monitor ibandronate and d3-ibandronate derivatives, respectively. A multiplexing LC system made possible the overlapping of two chromatographic runs, thus the interval between injections being reduced to only 2min, a very short analysis time for compounds of this class. The method was fully validated over the quantification range 0.2-175.0ng/ml, allowing an appropriate evaluation of the plasma concentrations of ibandronate, expected at therapeutic dosage, as proved by application to a pharmacokinetic study. A good linearity over the selected range (r>0.99), accuracy and precision within +/-15% of the target values and a recovery over 50% were obtained.