Seventeen corn samples, which formed part of a series of field trials conducted in Argentina, were analyzed for fumonisins Bi (FBi), B2 (FB2), and B3 (FB3). Combined fumonisin concentrations recorded in the samples ranged between 1585 and 9990 ng g-1. The bulk of the samples (16/17) had combined fumonisin levels in excess of 2000 ng g-1, with several having levels previously shown to be associated with outbreaks of equine leukoencephalomalacia. In addition, several isolates of Fusarium moniliforme and Fusarium proliferatum of Argentinian origin were analyzed to determine their fumonisin-producing ability. FBi was the major fumonisin analogue produced by the F. moniliforme isolates (50-8160 µg g-1), but for each isolate, production levels of FB3 exceeded the corresponding FB2 levels. One of the three F. proliferatum isolates produced only FB2. The data represent the first reports of the natural occurrence of the three major fumonisin analogues in Argentinian corn and the production of fumonisins by Fusarium isolates from Argentina.