We would like to take this opportunity of expressing our sincerest thanks to the many persons who have made adrenal tissue and related materials available to us for our work. Our especial gratitude is extended to Drs. J.J. Brown, A. Lever and J.I.S. Robertson of the M.R.C. Blood Pressure Unit, Glasgow, Dr. J.K. Grant, Royal Infirmary, Glasgow, Professor R.B. Welbourn and Dr. W. Kelly, Royal Postgraduate Medical School, Drs. D.B. Grant of Great Ormond Street, J. Ginsberg, Royal Free Hospital, D.C. Anderson, Hope Hospital, Salford, C.R. Edwards, St. Bartholomew's Hospital and Professor I. Doniach (for merly of the London Hospital) and Messrs. J.-c. Gazet, A. McKinna and P. Greening, Royal Marsden Hospital, London. The preparation and presentation of the material and the results would not have been possible without the help of Dr. P. Monaghan and his Electron Microscopy Unit, Ludwig Institute for Cancer Research (London Branch), Sutton, Mrs. Mitchell and her Histology Team, Royal Marsden Hospital, Sutton, Mr. K. Moreman of the Photographic Department of the Royal Marsden Hospital and Institute of Cancer Research, London and Mr. M. Hughes for graphics. Particular thanks are due for the untiring efforts and assistance ofMr. J. Ellis and Mrs. D. Corney of the Ludwig Institute for Cancer Research (London Branch), Sutton, for most of the photographic and secretarial work respectively. Professors G. Dhom and E. Mausle kindly provided material for Figs.