Black (Aphthona lacertosa and Aphthona czwalinae) and brown (Aphthona nigriscutis) flea beetles are among the more successful biological control agents used in the control and management of leafy spurge on a relatively large scale in the Northern Great Plains. The objectives of this study were to document leafy spurge population dynamics in response to control by black and brown flea beetles, determine the role of selected site characteristics on establishment and persistence of the beetles, and evaluate the general response of the resident vegetation to control of leafy spurge. In late June 1998, about 3 000 insects of each species were released into permanently marked plots in northwestern South Dakota and southeastern Montana. Beetle abundance, density and foliar cover of leafy spurge, and foliar cover of the resident vegetation were evaluated each year from 1998 through 2004. Black beetles increased rapidly and peaked at 65% of their measurable potential abundance within 2 years (P < 0.05) following release and dominated all release plots throughout the study. Although population growth characteristics of black flea beetles were highly variable, the successful patterns in reducing the dominance of leafy spurge were fairly consistent. By 2004, foliar cover of leafy spurge on both release and nonrelease plots was significantly reduced compared to prerelease values. Foliar cover of grass and grasslike plants increased concomitantly with the reduction in leafy spurge dominance while cover of forbs on release and nonrelease plots remained consistently below noninfested values.