A chemical test reported by Karr et al. (Plant Physiol. 55:727) to assay for host-specific toxin produced by Helminthosporium maydis race T was evaluated. Preparations from culture filtrates of both race T isolates, containing host-specific toxin, and similar preparations from race O isolates, containing no detectable host-specific toxin, gave positive reactions in the chemical assay. Also, preparations containing active or inactive toxin gave equal responses in this test. The procedure does not provide a reliable method for assaying H. maydis race T toxin.