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Medusahead [Taeniatherum caput-medusae (L.) Nevski], a non-native, winter-annual grass (Poaceae), has invaded rangelands throughout the western USA. Medusahead is an aggressive competitor that crowds out native plants and reduces forage for wildlife and livestock. Sulfometuron methyl is a sulfonylurea herbicide used to control medusahead, but its effect on non-target native forbs is largely unknown. We assessed the impact of an autumn application of sulfometuron methyl on native forbs on the sagebrush/bunchgrass steppe of eastern Oregon over 3 years. We applied 70ga.i./ha (1.0oz. a.i./acre) of sulfometuron methyl to randomly selected locations on three sites in a split-plot-in-time (repeated-measures) experimental design. Three years after treatment, 6 of the 11 forb species studied had a significant reduction in density (P less than 0.05), with densities ranging from 3 to 60% of the pre-treatment levels. The results of this study suggest that the benefit of medusahead control by sulfometuron methyl should be weighed against the damage to non-target species.