Distribution of the p53 pseudogene within the house mouse species (genus Mus) was studied with polymerase chain reaction for 37 individuals that were caught at different localities. Pseudogene-specific fragments were detected in some, but not all, individuals of Mus musculus subspecies regardless of locality and type of subspecies. In addition, 3 of 7 individuals belonging to different Mus species carried the pseudogene in their genomes. These results show the existence of an interspecific presence/absence polymorphism of the p53 pseudogene in mice. Sequence analysis of 11 amplified 0.3-kb fragments suggested that the pseudogene originated in an ancestral mouse about 7 million years ago. Thus alleles with and without the p53 pseudogene have persisted through the mice speciation. The evolutionary rate for the p53 functional gene was also estimated to be about 3.3 x 10(-9) per nucleotide site per year.