Analysis of the dreams of a patient who possessed the ability to awaken at a precise predetermined time led to the conclusion that he timed his dreams so that the security of knowing that his dreams would be interrupted by his alarm clock was used as a defence against the emergence of anxiety. Discussion of the problems raised by this observation leads to the hypothesis that 'the sleeper, confronted with the necessity of dreaming, seeks those conditions under which he can dream most safely, pleasurably, and with the least expenditure