Variation in DNA-content between species or cultivars within a cultivated crop are known and can be caused by differences in ploidy level or, at similar levels of ploidy, by taxonomic differences between genotypes. The first phenomenon is well-known in lilies. Differences in DNA content can be measured efficiently by using flow cytometry. Only a few milligrammes of plant material is sufficient for these DNA-determinations. Using flow cytometry it was possible to determine reproducibly the DNA-content of lilies with high precision. A large variation in DNA content between diploid lily species and cultivars was observed, up to a difference of 34␒n DNA content between L. henryi and L. canadense. Variation between cultivars was less pronounced. Interspecific hybrids had the intermediate DNA content of both parents. Therefore the technique is useful for very early identification of interspecific hybrids.