Cryopreservation Techniques for the long term storage of human erythrocytes are no longer limited to research laboratories but are now within the technical capabilities of many larger Transfusion Laboratories as part of routine blood banking. Reconstituted frozen blood has been used successfully in passive transfusions, for combating shock, in open heart surgery, for rapid transfusion of hypovolaemic anaemic patients, for long term maintenance in aplastic anaemia and for exchange and intrauterine transufions. This Thesis describes the history of this branch of cryobiology from its beginning in the 1950's until techniques were developed for preservation and viable recovery in the 1960's until today in the 1970's such techniques are well advanced. The advances in technique described in this Thesis represent a period of five consecutive years of study and application. Descriptions are given of in vitro and later in vivo work with emphasis on the problems and solutions to the introduction and operation of banks of frozen red cells in the West of Scotland and the contributions made to the United Kingdom capability.