Technical Abstract: An accurate greenhouse screening method has not previously been developed to identify host response to sheath blight disease caused by Rhizoctonia solani Kühn that causes significant economic losses in rice yield worldwide. The unavailability of a robust pathometric screening system in the greenhouse has made it difficult to quantify disease reactions to R. solani, and has hampered studies on the genetics of resistance and plant breeding efforts to improve resistance. In an effort to develop a standardized laboratory pathometric micro-chamber screening method to quantify resistance to R. solani in rice, five rice cultivars, representing a wide range of observed disease reactions under filed conditions, were examined in a blind inoculation test at three locations (Arkansas, Texas, and Colombia). Rice seedlings were inoculated at the 3-4 leaf stage with potato dextrose agar plugs containing mycelium and then covered with a 2 or 3 L transparent plastic bottle for maintaining high humidity after inoculation. Two cultivars Jasmine 85 and Lemont that have consistently been demonstrated to show the highest and lowest levels of resistance, respectively, in previous field and greenhouse studies were used as controls. Concurrent field experiments in Arkansas and Texas were also performed to compare the greenhouse disease ratings with those observed under field conditions. Overall, the relative disease ratings of the seven test cultivars were consistent between test locations and with field evaluations. Thus, the micro-chamber screening method can be used as an effective approach to accurately quantify resistance to the sheath blight pathogen under controlled greenhouse conditions and should help expedite the selection process to improve resistance to this important pathogen.