Twenty-five races and subraces^ of Puccinia graminis tritici were identified in 1, 005 isolates from 686 uredial collections. Races 56 and 15B comprised 31 and 30 percent, respectively, of the isolates; the 17-29 race-group^, 14 percent; race 11 (with 32), 13 percent; 38, 4 percent; 48A, 2 percent; 15, 1 percent. These races totaled 95 percent. The remaining 5 percent included 16 other races and subraces. Four races were identified in 38 isolates from 25 collections of rusted wild barley made in Minnesota, North Dakota, and South Dakota. Race 15B was isolated more frequently than races 11, 56, or 38. Seventeen races of wheat stem rust were isolated from 18 aecial collections. Races 56, the 17-29 race group, 11, 32, and 147 were isolated from two to four times each; other races once. Unusual races included 75, 118, 126, 142, and 147. Certain varieties of wheat were fovind to be useful as supplemental differen- tial varieties in distinguishing subraces. The varieties Triticimn timopheevi , C.I. 3255, and N. D. 3 (C 1. 13159) differentiated four subraces of race 11; the first two, with Tremez Molle, differentiated four subraces of 15B; and C. I. 3255, N.D.3, Towner, and R. L. 3206 differentiated five subraces of the 17-29 group. Conley, Yuma, and Langdon were resistant in the seedling stage to subraces of race 11 at temperatures of 65 , 75 , and 85 F and mostly resistant to sub- races of the 17-29 group at the same three temperatures. From 408 collections of P. graminis avenae , race 7 comprised 66 percent of the 476 uredial isolates identified. Race 7A decreased from 4. 5 percent in 1955 to 2 percent in 1956. Race 2 (with 5) comprised 17 percent of the isolates; race 8, 14 percent. Four races were identified in six aecial collections. One of the isolates is a new subrace to which Bond is moderately resistant. This is the first indication, so far as known, that Bond has a gene or genes for resistance to stem rust.

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