The purpose was to test the effects of sleep loss upon performance. Tonus acts as compensatory mechanism during effort, fatigue, and distraction. Autogenic reinforcements following loss of sleep were found. Four performance tests consisting of finger oscillation, discrimination reaction, manual pursuit, and memory span were given to two subjects. While efficiency of performance may remain at the same level the tonus accompaniments of the work are higher for days following serious loss of sleep. A higher degree of tension tendered to accompany night work which equalled the efficiency of morning performance. The cumulative effect of prolonged sleep loss tended to destroy the efficacy of tonic muscular compensation. (PsycINFO Database Record (c) 2006 APA, all rights reserved)