In this short survey the main, available information on the molecular mechanisms of action of heavy ions on DNA is critically reviewed. Formation of single- and double-stranded DNA breaks in cells exposed to heavy particles is well established. On the other hand, base damage and, in a more general way, clustered lesions, whose formation should be increased upon exposure to heavy ions, have not yet been isolated and characterized. Efforts should be made to identify this important class of DNA damage in both isolated and cellular DNA. Sensitive and specific assays involving chemical and biochemical approaches have to be developed for such a purpose.