The usefulness of random amplified polymorphic DNA (RAPD) in characterizing two perennial ryegrass (Lolium perenne L.) synthetic cultivars, `Accolade' and `Caravelle', was tested. Two out of 10 arbitrary primers produced three RAPD markers that distinguished bulk samples of 30 seedlings. Additional fragments were apparent when DNA from individual seedlings was amplified. Amplification products from bulk samples were not simply the sum of amplification products of individual seedlings and did not reflect all the diversity within or between the cultivars. The study illustrates the need to screen individuals to accurately evaluate the genotypic composition of a synthetic cultivar or heterogeneous population.