Technical Abstract: We examined the effect of saccharin on the systemic acquired resistance (SAR) response of soybean to the fungus Phakopsora pachyrhizi, the causal agent of soybean rust. Plants were grown hydroponically in half-strength Hoagland’s solution and were challenged with the pathogen 1, 5, 10 and 15 days after treatment with 3 mM saccharin applied either as a foliar spray or a root drench at the 2nd trifoliate (V3) and early reproductive (R1) stages. Plants were destructively harvested and assessed for visible rust symptoms 2 weeks after inoculation with the pathogen. Mode of saccharin applications were significant factors influencing the severity of rust infection. Saccharin applied as a root drench was more effective than the foliar spray treatment at inducing SAR, with increased resistance observed 1 day after application. Systemic protection against rust infection was still apparent 15 days after application of saccharin as a root drench. In contrast, foliar treatment with saccharin did not increase systemic protection until 15 days after treatment. When systemic protection was induced by the application of saccharin in either manner, there was no significant reduction of plant growth except when saccharin was applied as a drench 15 days after treatment at the R1 stage of development.