I must protest against the knowing groans expended every time a scientist is personally affronted by the image of a left-handed DNA helix (Nature 467, 401; 2010). I would remind the groaners that DNA handedness depends on its molecular sequence — witness a seminal paper you published more than 30 years ago: 'Molecular structure of a left-handed double-helical DNA fragment at atomic resolution' (A. H.-J. Wang et al. Nature 282, 680–686; 1979).