USING oligonucleotide primers designed to match conserved regions of mammalian mitochondrial DNA (mtDNA)(1), we have amplified and sequenced two divergent cytochrome b nuclear pseudogenes from orangutan cellular DNA. Evolutionary analysis suggests that a nuclear transfer occurred about 30 million years ago on the lineage leading to the catarrhines (Old World monkeys and hominoids), and involved a long (at least 3 kilobases), probably damaged, piece of mtDNA. After this transfer, the pseudogene duplicated, giving rise to the two copies that are probably present in all hominoids, including humans. More recent transfers involving the entire cytochrome b gene have also occurred in the Old World monkeys. Such nuclear copies of mtDNA can confound phylogenetic and population genetic studies(2-4), and be an insidious source of DNA contamination of ’ancient’(3,5) and forensic DNA. Indeed, contamination with these anciently transferred human pseudogenes(5) is almost certainly the source of the cytochrome b sequences recently reported from ’dinosaur bone DNA’(6).