Leaf rust of wheat (Tril icum aestivum and T. durum) caused by Puccinia recondita f. sp. tritici was first observed on June 9 in southern Manitoba. The disease had an uneven distribution in 1988 due to the extreme heat and drought conditions that prevailed over North America. Forty-four virulence combinations of P. recondita were detected in 1988 using 15 isogenic Thatcher backcross lines as differentials. Virulence was not detected to resistance genes Lrl9, Lr21, Lr25, and Lr29. In Manitoba and Saskatchewan, incidence levels of virulence to Lr24 and Lr26 increased significantly, while incidence levels of virulence to Lr9 and Lr16 remained extremely low. The leaf rust population in the prairie region was dominated by three virulence combinations; the populations in eastern Canada and British Columbia were more diverse.