There is currently a need for a technique to detect chlorinated aromatics in the gas phase, for example in the exhaust stream of an incinerator. This paper presents the results of investigations into a laser-based scheme that is ultrasensitive, species- and isomer-selective. and quasi-real-time. The approach is to use free-jet-expansion cooling to narrow the resonantly enhanced multiphoton ionization (1+1 REMPI) spectrum and to allow isomerically selective laser excitation via the first electronically excited singlet state. The photoions are mass analyzed in a reflectron time-of-flight mass spectrometer (TOF MS) that has a resolution (M/ΔM) of ∼600 at mass 150. Ppb level detection limits with complete isomeric selectivity are achieved for the dichlorobenzenes using the jet-cooled REMPI/TOF MS technique. The applicability of this detection scheme to more complicated toxic species, such as PCB's, dioxins, and furans, are discussed and ideas for a device that could be used for quasi-real-time detection in a typical working environment are presented.