Many real and potential hazards will face astronauts* during operations in space. Some of these hazards might be of little medical significance; others might produce serious medical problems. This book is an initial attempt to describe the characteristics and suggest the management of possible medical problems which might arise from hazards of space operations. Attention is not given here to the so-called 'naturally occurring' diseases. Writing is oriented to future interplanetary missions during which, due primarily to the time required to return to earth, the diagnosis and definitive or interim treatment of medical problems will have to be carried out in space. It is therefore assumed that suitable diagnostic and treatment facilities and medically trained personnel will be available on advanced spacecraft, in which large, multidisciplined crews will be living in a comfortable, 'shirt-sleeves' environment. To lay the groundwork of Space Clinical Medicine, a field in which very little has been written and essentially no experience gained to date, it was found necessary to consider clinical manifestations, diagnosis, and treatment of possible medical problems in space. Wherever necessary, various hazards of space operations are defined and analysed in order to determine their possible medical effects. The patho physiologic characteristics of medical problems are discussed, frequently in detail, to provide the rationale for their prevention and treatment.