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The presence or absence of heterozygous individuals and overall genetic variation were determined for the invasive exotic annual grass Bromus tectorum from four populations in northern Nevada using seven species-specific polymorphic di-nucleotide microsatellite markers. Allelic polymorphisms were found in all populations, but not at all loci within each population. Mean genetic diversity across loci within populations ranged from 0.009 +/- 0.006 to 0.551 +/- 0.073, across populations x = 0.234 +/- 0.043. Fifteen individuals from the total sample (8.24%) were heterozygous at 1-4 loci. Two populations exhibited no heterozygosity and the remaining two populations had relative heterozygote proportions of 22.5% and 12.1%. Facultative outcrossing is discussed as an aspect of reproductive plasticity in cheatgrass and as a mechanism promoting the evolution of invasive genotypes.