Nocturnal sleep was recorded prior to daytime testing that included the Multiple Sleep Latency Test, profile of mood states, card sorting, and Stanford Sleepiness Scale in 138 volunteers with the complaint of chronic insomnia and 89 noncomplaining sleepers ("normals"). In both groups daytime sleep tendency had no significant linear correlation either with any Minnesota Multiphasic Personality Inventory scale or with tension/anxiety and other moods assessed in the morning. In normals, speed of card sorting but not subjective sleepiness tended to correlate with sleep tendency. Given that physiological sleepiness is the most predictable consequence of sleep deprivation in normals, it is particularly interesting that 14% of the insomniac group are chronic insomniacs with no measurable daytime sleep tendency. Despite this lack of sleep tendency during the day, their nocturnal sleep was just as poor as insomniacs with greater daytime sleep tendency. The lack of daytime sleepiness seen in this subgroup may reflect a basic pathophysiological aspect of their insomnia.