DNA sequence data from 2 nuclear introns (mitochondrial malate dehydrogenase intron 7 and acid phosphatase type V intron 2) were collected for 9 taxonomic units of rodents, 8 of which were in the genus Mus. Data were used to infer phylogenetic history of the 9 taxa, which was then compared with a consensus phylogeny taken from previous literature. In general, the nuclear intron data provided strong support (bootstrap proportions > 80) for relationships accepted in the consensus tree. The intron data disagreed with previous mitochondrial data in that 2 M. m. domesticus sequences were paraphyletic with respect to M. m. castaneus and M. m. musculus. This paraphyly, if real, likely reflects the longer lineage-sorting time of the nuclear genome compared with the mitochondrial genome. Introns seem to provide an attractive source of nuclear DNA sequence data for phylogenetic analysis, but mitochondrial data are likely to be superior for very recent divergences.