The aim of this study was to develop a protocol for the detection of the pesticides atrazine and alachlor in water at concentrations below .1 mg/l using immunochemistry. Detection below these concentrations may be useful in identifying trends of increased pesticide contamination before there is a real health risk. The procedure involved using a sample routinely processed for gas chromatograph (GC) analysis and evaluating by immunoassay after evaporating off the solvent and resuspending the sample in water. The study results found immunoassay is only slightly less reliable than GC analysis. Concentrated organic extracts prepared for GC analysis can also be successfully used for the detection and quantitation of atrazine and alachlor by immunoassay analysis at concentrations significantly below the detection limit of GC. Method detection limits for atrazine were calculated at approximately 0.4 ng/l -a 250 fold improvement over GC, and approximately 0.3 ng/l for alachlor- a 300 fold improvement over GC. This procedure is being used in a study investigating the levels of atrazine and alachlor in rain water.