Corn silage was dried, ground, and then extracted with 0.1 M ethylenediaminetetraacetic acid. The filtrate was applied to a FumoniTest immunoaffinity column. Fumonisins were derivatized with naphthalene-2,3-dicarboxaldehyde, separated on a C(18) liquid chromatographic column, and detected by fluorescence. The detection limits for fumonisin B(1), fumonisin B(2), and fumonisin B(3) were 50, 25, and 25 ng/g of dried silage, respectively. Recoveries of fumonisin B(1), fumonisin B(2), and fumonisin B(3) from wet and dried corn silage spiked over the range of 100-5000 ng/g averaged 91-106%. The method was applied to corn silage samples collected from the midwestern area of the United States during 2001-2002. Of 89 corn silage samples, fumonisin B(1), fumonisin B(2), and fumonisin B(3) were found in 86 (97%), 64 (72%), and 51 (57%) of the samples. The mean positive levels of fumonisin B(1), fumonisin B(2), and fumonisin B(3) were 615, 93, and 51 ng/g, respectively, in dried silage. This suggests that fumonisins may be frequent low level contaminants in corn silage.