SUMMARYTwo ascospore progenies from a cross between two obligately heterothallic isolates ofCochliobolus spieiferwere found to be sexually compatible with both mating types although self-sterile, and were termed“dual compatible.”All matings between dual compatible isolates were fertile and all ascospore progeny derived from crosses of dual compatible isolates and heterothallic isolates were fertile with the dual compatible parent. Genetic analyses of first and second generation dual compatible isolates gave dissimilar segregation patterns. Segregation patterns for one ascospore isolate followed a 1:1:1 ratio for mating types ofA: a: dual, respectively. The second ascospore isolate followed a 1:2:1 segregation ratio for two generations for mating types of nonparental: parental: dual, respectively. The dual mating capacity does not appear to conform to any previously described sexual mechanism in the fungi.