Bioassay-guided fractionation is a technique that searches for active compounds in a mixture by separating the mixture and then determining the biological activity of each component. This is often performed through a series of successive separations and assays. Dynamic isoelectric focusing (IEF), a new technique invented in our lab, allows many distinct fractions to be collected from a sample. The ability to fractionate a sample, and then select the desired fractions and separate these fractions repeated times allows for a thorough search for the proteins that are active. Preliminary data shows that dynamic IEF can fractionate a sample into more than one thousand unique fractions, which should permit the identification of each protein in a fraction. The goal of this research is to identify proteins involved in the soybean-fusarium virguliforme interaction that cause foliar damage and death of the soybean. Fusarium culture medium has been shown to produce sudden death syndrome symptoms in soybeans when tested both by the foliar assay and by stem-cutting assays. This means that the toxin is secreted by the fungi and remains active for some period of time in solution. Dynamic IEF fractionation will allow us to separate the samples into more distinct fractions than possible by other fractionation methods, and will allow us to identify the active proteins causing the damage to the soybeans. Dynamic IEF and its application to fractionation will be described in addition to preliminary toxicity data from various fusarium culture fractions.