The natural rate of root cortical death (RCD) in seminal roots was investigated in different cereals by staining the roots with acridine orange. In all cereals investigated the part of the cortex having stainable nuclei gradually decreased with increased age of the root. Wheat differed from barley, oats and rye in having a much faster rate of RCD In 15-d-old root regions of wheat grown in soil, only 10–20% of the radius of the root had stainable nuclei. In barley, oats and rye the amount of cortex with stainable nuclei varied between 65 and 80% Minor differences in RCD were found between different barley cultivars or accessions. Large variation in RCD was found between different Triticum species: T. monococcum, T. dicoccum and different Aegilops species had much slower RCD than did hexaploid wheat. These results are discussed in relation to microbial colonization of roots and susceptibility to root pathogens.