The impact of the herbicide, hexazinone, was assessed on aquatic macrophytes, aquatic and terrestrial invertebrate communities within forested watersheds in the Piedmont region of Georgia. Four replicate watersheds received hexazinone on April 23, 1979, and were subsequently monitored for eight months. Residue levels in terrestrial invertebrates were a maximum of two orders of magnitude greater than comparable levels (0.01 to 0.18 ppm) found in forest floor material. Aquatic organisms in a second order perennial stream were exposed to intermittent concentrations of hexazinone (6 to 44 ppb). Hexazinone and its metabolites were generally not detected (less than 0.1 ppm) in aquatic invertebrates and macrophytes. No major alterations in species composition or diversity were detected in the aquatic macroinvertebrate community. Terrestrial microarthropod samples collected near the end of the study period revealed no major community changes.