Ten insomniacs and controls, in whom major physiologic disorders such as sleep apnea and nocturnal myoclonus were ruled out, underwent studies of sleep, temperature motor activity, cognitive performance, and perception of depth of sleep. Subjective descriptions of sleep differed significantly between insomniacs and normals on a variety of variables. In contrast, polysomnographic evaluation showed increased intermittent waking time and decreased sleep efficiency, and only a tendency toward decreased total sleep and increased sleep latency. Core temperature during sleep tended to be slightly higher than in controls, with no evidence of phase shift. MMPI evaluation revealed that insomniacs had higher scores on the F, D, and SI scales, and lower values on the K scale. On cognitive testing, insomniacs did well on tests of episodic (recent) memory, but displayed major deficits in accessing semantic memory (retrieval of material already known). Compared to normals, insomniacs described REM sleep as relatively "light" sleep.