Technical Abstract: Chromosome rearrangements between fungal strains may reduce fertility in sexual crosses through the production of genetically inviable recombinant progeny. As such, rearrangements can be important postzygotic reproductive barriers that contribute to the speciation process. The presence of chromosome rearrangements in crosses with Gibberella zeae was tested by counting asci with 8, 6, 4, or 2 viable ascospores. Counts were made by observing rosettes of asci extruded from crushed perithecia and by observing unordered ascospore tetrads ejected onto agar slabs from mature perithecia. The two methods gave similar results. Self-fertilized cultures served as controls and produced the normal eight ascospores per ascus in >98% of cases. Crosses with strains known to carry chromosome rearrangements produced significant frequencies of asci with 6, 4, or 2 ascospores, as expected. These results suggest that these methods will be useful to survey populations of G. zeae for chromosome rearrangements.