Many subjects (Ss) anticipate that perceptual isolation will be an occasion for pleasant rest, an opportunity to make money by doing nothing, or a chance to commune with their inner selves, but few find it an exhilirating experience. Emotional reactions generally range from boredom to panic. Sources of stress are not as obvious as in stress situations involving electric shock or threat to the ego. This paper will attempt to analyze possible sources of stress within the situation and personalities of Ss by reviewing the results of a number of studies. Data on reported visual and auditory sensations were reviewed in a previous paper66 and will not be treated extensively here. There will be no direct discussion of the cognitive and perceptual effects of isolation as meas ured by laboratory tests. The paper will concentrate on endurance of subjects in isolation, verbal reports during and