Coal combustion products (CCPs) have potential for use as soil amendments on acidic soils. One concern for plants grown on acidic soils amended with CCPs is boron (B) toxicity, since many CCPs contain considerable B. Maize (Zea mays L.) was grown (greenhouse) on acidic soil [Umbric Dystrochept, pH 3.9 (1 soil:1 10 mM CaCl2)] amended with 15 CCPs [two fly ashes (FAs), three fluidized bed combustion products (FBCs), one calcium (Ca) oxide (CaO) material, six high Ca sulfite (CaSO3) flue gas desulfurization products (FGDs), and three high Ca sulfate (CaSO4) FGDs] at different levels to determine accumulation of B in shoots. Plants were also grown in soil amended with Ca carbonate (CaCO3, lime) and chemical grade CaSO4 and CaSO3 as controls. Among the CCPs tested, FAs contained the highest B levels. Shoot B concentrations were as high as 500 mg kg(-1) without reductions in dry matter (DM) for plants grown on soil amended with one FA. Plants grown with one FBC had sufficient B to suspect potential B toxicity, and plant DM was greatly reduced or died when grown with > 0.5% of this material. Relatively high shoot B concentrations were noted in plants grown with the highest levels of high CaSO3 FGDs. High shoot B concentrations (similar to 300 mg kg(-1)) were noted for plants grown with > 5% levels of one high CaSO4 FGD, and DM declined after reaching these levels. Plants grown on soil amended with CaO had low shoot B. Some of the CCPs used in this study contained sufficient B to potentially induce B toxicity in plants grown on the acidic soil amended with the various CCPs. Maize growth was generally enhanced when grown on soil amended with the CCPs at appropriate levels.