Neurobehavioural performance deficits associated with sleep loss have been extensively studied, in particular, the effects on psychomotor performance. However, there is no consensus as to which, if any, cognitive functions are impaired by sleep loss. To examine how sleep loss might affect cognition, the automatic processes supporting word recognition were examined using the masked priming paradigm in participants who had been exposed to two consecutive days of sleep restriction. Twelve healthy volunteers (mean age 24.5 years) were recruited. Nocturnal sleep duration was restricted to 60% of each participant's habitual sleep duration for two consecutive nights by delaying scheduled time of sleep onset and advancing time of awakening. In controlled laboratory conditions, participants completed the Psychomotor Vigilance Task and Karolinska Sleepiness Scale and a masked priming word recognition task. As expected, significant increases in subjective sleepiness and impaired psychomotor performance were observed after sleep loss. In contrast, response times and error rate on the masked priming task were not significantly affected. However, the magnitude of the masked priming effect, which can be taken as an index of automaticity of lexical processing, increased following sleep loss. These findings suggest that while no evidence of impairment to lexical access was observed after sleep loss, an increase in automatic processing may occur as a consequence of compensatory mechanisms.