Isolated nuclei from cereal plants were used for quantitative determination of DNA per nucleus by flow cytometry. The technique is based on enhanced fluorescence of ethidium bromide and olivomycin when they bind to DNA. Nuclei were isolated from protoplasts derived from leaves of seedlings. The diploid Hordeum vulgare cv. Trumpf was used as an internal standard. Analysis of nuclei from several cultivars of hexaploid wheat (Triticum aestivum), Triticum durum var. hordeiforme, T. durum var. alexandrinum, Triticum araraticum, Triticum timopheevi, Triticum monococcum, Aegilops speltoides, Secale cereale, and one hexaploid and one octoploid triticale revealed significant intra- and inter-specific differences in DNA values per 2C nucleus. The advantages of the procedure are discussed along with its utilization for quantitative DNA measurement in Gramineae.Key words: nuclear isolation, flow cytometry, DNA content, cereals.