Various approaches to the study of physiological and behavioural effects of energy deprivation are presented and discussed. An experimental, total energy deprivation in 20 healthy human volunteers during an 11-day period, preceded and followed by 4-day control periods, is described. Potentially pathogenic reactions which occurred in spite of precautions are analysed. It is concluded that the present controlled real-life model with acute total energy deprivation serves the purpose of studying hypotheses concerning potentially pathogenic mechanisms occurring in deprivational situations under conditions of natural and man-made catastrophes.