A continuous flow fluorescence based immunosensor has been developed at the Naval Research Laboratory as an inexpensive, field portable device to detect environmental pollutants. Detection of environmental pollutants such as explosives [e.g. trinitrotoluene (TNT) and hexahydro-1,3,5 trinitro- 1,3,5-triazine (RDX)[ and polychlorinated biphenyls (PCBs) have been achieved at low level concentrations. The continuous flow immunosensor (CFI) employs antibodies as recognition elements for specific antigens. Antibodies specific for the environmental pollutants of interest are covalently immobilized on a solid support matrix. Subsequent saturation of the antibody-support complex with a fluorescence analog (i.e. cyanine dye) of the pollutant completes the sensor matrix. The derivatized matrix is prepacked into a micro column with a continuous flow stream of buffer that removes nonspecifically bound fluorescent analog. After a stable baseline is obtained sample injections of the desired pollutant (PCBs, TNT, RDX, etc.) into the flow stream displaces the fluorescence analog from the immobilized antibody on the solid support. A signal response over background from the displaced fluorescence analog is measured and integrated by an in-line fluorometer. Dose response curves reveal the lowest limit of detection for TNT and RDX is 20 ppb (parts-per-billion). Detection limits for PCBs is slightly higher at 1.0 ppm (part-per-million). Results from field trials conducted at two military bases, Umatilla Army Depot (Hermiston, Ore.) and Site F and A at Naval SUBASE Bangor (Bangor, Wash.) demonstrated the capabilities of the immunosensor in performing on-site field analysis in groundwater and soil leachate matrices.