[en] α-particles, which are ionising radiation of high linear-energy-transfer emitted, for example, from radon or plutonium, pass through tissue as highly structured tracks. Single target cells in the path of the tracks might be damaged by even low-dose α-irradiation. We found non-clonal cytogenetic aberrations, characterised by a high frequency of chromatid aberrations with chromosome aberrations, in clonal descendants of haemopoietic stem cells after exposure to α-particles of bone marrow cells from two of four haematologically normal individuals (up to 25% abnormal metaphases). The data are consistent with a transmissible genetic instability induced in a stem cell resulting in a diversity of aberrations in its clonal progeny many cell divisions later. (author)