Fifty-seven cultivars and selections of perennial ryegrass (L. perenne) and 1 selection of annual ryegrass (L. multiflorum) were screened under greenhouse conditions for resistance to the crown rust fungus (Puccinia coronata f. sp. lolii). Variation in resistance to crown rust among entries was dramatically evident, which indicated a potential for developing ryegrass cultivars with improved resistance to the crown rust fungus. Frequency distributions based on rust reaction of cultivars provided insight into the type of resistance and mode of inheritance. Bimodal distributions based on rust reaction were indicative of major genes undergoing segregation. The advantage of using frequency distributions when evaluating germ plasm for resistance to pathogens in cross-pollinated populations is discussed.