Heterothallic isolates of Pyricularia pathogenic on different hosts were used to demonstrate experimentally the genetic segregation of factors for pathogenicity and mating type through the perfect stage. The pathogenicity of 325 monoascosporic progeny from the crosses of Pyricularia isolates from weeping lovegrass and finger millet to the original hosts segregated 136:127:26:36; pathogenic to weeping lovegrass alone, finger millet alone, both weeping lovegrass and finger millet, and nonpathogenic to both hosts, respectively. Based upon a 1:1 segregation, the pathogenicity to weeping lovegrass or finger millet seems to be conditioned by a single gene. The results suggest that factors for pathogenicity to two hosts are conditioned by different genes located at different loci on homologous chromosomes. Mating type was inherited independently of pathogenicity. Pathogenicity and mating type were determined for eight ascospores from a single ascus. Judging from the ascospore analysis and the previous cytological study of the ascus, it seems that factors for pathogenicity and mating type are conditioned by chromosomal genes.