Air sampling of isocyanates with 2-MP coated filters is a well-established method where the isocyanate derivative is analyzed by HPLC with combined UV/electrochemical detection. We have investigated the possibility to use HPLC with tandem mass spectrometry (LC-MS/MS) for detection and quantification with enhanced selectivity and sensitivity. Qualitative analysis of 2-MP derivatized diisocyanates was performed with full scan and the spectra contained a protonated molecule with a dominant fragment containing the 2-MP derivative. The same fragmentation was obtained in the daughter ion spectra from the molecular ion and was selected as target for selected reaction monitoring (SRM). Linear detection with SRM was obtained between 5 pg and 5 ng injected amount. Corresponding LC-UV analysis is in our laboratory performed in a range of 300 pg - 30 ng injected amount. The signal to noise ratio in LC-MS/MS from 50 pg is ranging from 10 – 200 depending on which of the diisocyanates that is analysed. Ten times that amount (500 pg) analyzed by LC-UV gives a signal to noise ratio that ranges from 14 to 40, depending on the compound. We analyzed samples collected at workplaces containing TDI, MDI and HDI with LC- MS/MS, using electrospray ionization with multiple reaction monitoring. Those results were compared with the results from HPLC-UV. The MS/MS analysis gives better selectivity with regard to interfering substances. The method was further developed to include a wide range of mono and diisocyanates with possibility to screen for oligomers.