Numerous investigations demonstrated superior verbal memory performance after retention intervals of nocturnal sleep as opposed to diurnal wakefulness. However, it is not clear if the effect is attributable to either sleep or circadian phase. The present study therefore examined verbal recall after retention intervals of nocturnal sleep, diurnal wakefulness, and nocturnal wakefulness (sleep deprivation). Forty university students (range 19-30 years) were randomly assigned to one of the three conditions and were tested for cued recall of a paired-associate list 7 h after original learning. In line with previous findings, subjects in the nocturnal sleep condition expressed superior recall when compared to subjects in the diurnal wakefulness condition. However, contrary to predictions, recall performance between the nocturnal sleep and the nocturnal wakefulness condition did not differ significantly. The results raise some doubt on the generalizability of the beneficial effect of sleep on memory.