A method for the early detection and diagnosis of common bunt, caused by Tilletia tritici, has been developed. The technique is based on a nested PCR amplification of DNA from T. tritici in infected plant inflorescence tissue at the stage of internode elongation. Primers amplifying a 212 bp fragment in T. tritici were designed on the basis of sequences in the ITS2 region in the ribosomal RNA genes. Disease diagnosis obtained with nested PCR amplification correlated well with the conventional disease diagnosis, which involves manual observation of disease symptoms at maturity. With the present method, wheat varieties can be screened for resistance towards common bunt at the first node stage. There was no variation between the ITS2 region from T. tritici, T. laevis, T. controversa, and T. bromi and the primers are therefore not species specific. The PCR diagnosis method has only been validated for common bunt caused by T. tritici, but it is likely also to be applicable to T. laevis and T. controversa.