Seed dormancy allows weed seeds to persist in agricultural soils. Wild oat (Avena fatua L.) is a major weed of cereal grains and expresses a range of seed dormancy phenotypes. Genetic analysis of wild oat dormancy has been complicated by the difficulty of phenotypic classification in segregating populations. Therefore, little is known about the nature of the genes that regulate dormancy in wild oat. The objectives of our studies were to develop methods to classify the germination responses of segregating wild oat populations and to find molecular markers linked to quantitative trait loci (QTL) that regulate seed dormancy in wild oat. RAPD markers OPX-06 and OPT-04 explained 12.6% and 6.8% respectively, of the F(2) phenotypic variance. OPF-17 was not significant in a simple regression model, but it was linked in repulsion to OPT-04. A three-locus model of seed dormancy in wild oat is presented based on the 41-day germination profiles of F(1), F(2), F(3), BC(1)P(1)F(1), BC(1)P(1)F(2), and BC(1)P(2)F(1) generations, and the 113 day germination profile of 126 F(7) recombinant inbred lines. Loci G (1) and G (2) promote early germination, and the D locus promotes late germination. If at least one copy of the dominant G (1) or G (2 )alleles are present regardless of the genotype at D locus, then the individual will be nondormant. If the genotype is g (1) g (1) g (2) g (2) D_, then the phenotype will be dormant.