Procedures for studying isolation vary, and there is no typical laboratory isolation. The degree of contact between the isolated subject and his environment, especially his observers, must be defined in terms of distances, times, limitations of visual, auditory, and kinesthetic inputs, means available to the subject for structuring his isolated existence, and especially his ability or inability to terminate isolation when he wishes. Communication of any kind counteracts the effects of isolation, and when subjects know they are being observed they do not feel truly isolated. If communication or feedback to the subject is distorted, the situation becomes more stressful, and profound feelings of anger and anxiety can be produced. Experimentation in this field yields new data on individual differences, reveals the generally felt need of people for a structured environment, and is of importance in military medicine.