Utilization of the picosecond (100 ps) laser ionization was successful in measuring the mass spectra attributed to di-, tri-, tetra-, penta-, and hexa-chlorinated biphenyls. It was confirmed that the quantitative limit of this method in real-time (1 min) was 10 mu g/m(3)N (equivalent to 1/10 of the value established as the statutory limit for PCBs in the ambient air of the workplace environment). Further evaluations of measurement accuracy based on comparisons with the results of the conventional method (gas sampling and GC-MS) demonstrated a coefficient of variation within 30%. We undertook the measurement of the exhaust gas and the work environment atmosphere in PCBs treatment plants using the LI-IT-TOFMS method, confirming that the monitoring system could be operated appropriately by the introduction of an internal standard gas (2,4-dichlorinated toluene), and that it was possible to make continuous longterm measurements for over 500 h (total measurement time, > 6000 h).