There is substantial evolutionary evidence for gene transfer from the chloroplast to the nucleus. In an Advanced Online Publication in Nature Huang et al. report the results of experiments designed to measure the rate of transfer of chloroplast DNA (cpDNA) into the nucleus in Nicotiana tabacum tobacco plants (Nature, 5 February 2003, doi:10.1038/nature01435). They engineered the chloroplast genome by inserting a neomycin phosphotransferase reporter gene (neoSTLS2) that confers kanamycin resistance only when it is transposed to the nucleus. A screen of 250,000 seedlings led to the isolation of 16 kanamycin-resistant plants that showed stable inheritance of neoSTLS2. Huang et al. estimate the rate of cpDNA transfer as one transposition event in about 16,000 pollen grains.