Prior work has reported on the usefulness of fiber optic sensors in the detection of dissolved aromatic organic ground water contaminants such as the benzene, toluene, ethylbenzene, and xylenes (BTEX) fraction of petroleum fuels. Our device is a laser fluorimeter using fiber optic sensors for in situ measurements. Fluorescence intensity and lifetime can be measured at any wavelength in order to compare concentrations and discriminate certain compounds. Our instrument configuration uses a pulsed Nd:YAG laser twice frequency doubled to provide 266 nm excitation light. Excitation light, and subsequent induced fluorescence, are carried to the location of interest by a pair of 600 micron core fused silica optical fibers. Fluorescence is measured using a photomultiplier (PMT). PMT output goes either into a high-speed oscilloscope for fluorescence lifetime measurements or into a gated integrator for fluorescence intensity measurements. The same system can be used to detect aromatic contaminants in the vapor phase. Phenol, toluene, and xylene have been tested in the vapor phase. Concentrations below 10 micrograms phenol per liter air are detectable. In the vapor phase, the water Raman line seen around 295 nm in aqueous solution is insignificant, allowing a greater wavelength range to be scanned by the detector. Fluorescence spectra, fluorescence lifetimes, and fluorescence versus concentration information are presented. Applications of this approach to vadose zone ground water monitoring are discussed.