There is evidence for substantial transfer of mitochondrial DNA (mtDNA) to the nuclear genome in plants. Analysis of the recently completed Arabidopsis thaliana genome sequence indicated a mtDNA insertion of 270 kilobases (kb), larger than previously described mitochondria-to-nuclear DNA insertions. In the April 24 Proceedings of the National Academy of Sciences, Stupar et al present a detailed cytological characterization of the mtDNA insertion in chromosome 2 of A. thaliana (Proc Natl Acad Sci USA 2001, 98:5099-5103). Using fiber-fluorescence in situ hybridization (fiber-FISH) they show that the insertion is about 620 kb, or 2.3 times the size estimated in original measurements. The authors suggest that the complex and repetitive nature of inserted mtDNA can result in misleading estimates of insert length, and that fiber-FISH offers a high-resolution tool for genome analysis.