A 68 year old female who presented with long-term thrombocytopenia was clinically diagnosed as having chronic idiopathic thrombocytopenia purpura (ITP). Increased levels of the tumour suppressor p53 protein were detected by immunohistochemistry in the neutrophils and some monocytes of the peripheral blood preparation using the antibody DO-1, recognizing mutant and wild type p53 protein conformations. However, no positive staining in the peripheral blood samples from 41 myelodysplasias (MDS) and six normal individuals was observed. Single-stranded conformational polymorphism analysis performed on DNA extracted from the cytospin preparations from this patient indicated no mutations in exons 5-8 of the p53 gene. This report describes the unusual detection of elevated p53 protein in a non-neoplastic condition by immunohistochemistry using the antibody DO-1. This unexpected finding raises the possibility of classifying such patients as early MDS on the basis of their p53 status.