Immunoassay has become a common method for the screening of environmental samples. The purpose of this study was to determine the applicability of using an immunoassay to monitor atrazine concentrations in the Potomac watershed. The study demonstrated that immunoassay can be a cost effective technique for monitoring atrazine concentrations in a timely manner. The ease of use of testing atrazine by immunoassay was also evident in this study. The operator, who had no previous experience with immunoassay methodology, was able to obtain accurate results in the first attempt. The false negative rate was zero in this study as would be expected. The false positive rate was higher than desired. However, the immunoassay results were compared to the total of only atrazine and simazine concentrations by GC. The most likely explanation for this would be the presence of other triazine compounds or metabolites in the samples that were not quantified by GC/MS. This study shows that this immunoassay can be an effective tool for monitoring atrazine and triazine herbidides in water. Includes 2 references, tables.