We have examined p53 alleles in 151 DNAs from patients with myelodysplastic syndrome using single-strand conformation polymorphism analysis of polymerase chain reaction products. We focused our study on the four highly conserved regions of the p53 gene and detected five patients with aberrantly migrating fragments. We confirmed the putative mutation in each case by direct sequencing analysis. Of these five patients, three had chromosome 17 monosomy associated with p53 mutation, one patient showed one mutated p53 allele and one wild-type allele, and the last patient demonstrated only the mutant allele, suggesting a homozygous state. Unlike many other types of human cancers, point mutations in the p53 tumor-suppressor gene appear to be a rare event in myelodysplastic syndromes.