THIS note refers to the communication from Dr. E. H. Kleisner de Galan1 which contains evidence which is said to be contrary to our findings2–5 that ageing in man is associated with an increasing frequency of lymphocytes with an abnormal sex chromosome complement, as determined from the examination of blood cultures. Our findings were substantiated by Hamerton et al.6 from an examination of members of the population of Tristan da Cunha when they were temporarily evacuated to Britain. More recently added support has come from the work of Kerkis and Rajabli7 at the Institute of Cytology and Genetics at Novosibirsk.