1 Effects of prolintane (15 and 30 mg) and pemoline (60 and 100 mg) on sleep were studied in six healthy adult males. Sleep was assessed by electroencephalography and by analogue scales. 2 Prolintane (15 and 30 mg) reduced rapid eye movement (REM) sleep both by delaying the first period (P < 0.05 and < 0.001 respectively) and by reducing total REM sleep (P < 0.05 and < 0.001 respectively). In some subjects there were increased awakenings during the early part of the night, and in two subjects long periods of wakefulness occurred. 3 With pemoline (60 and 100 mg) sleep duration was marked reduced (P < 0.001). There was evidence in some subjects of delay to the first REM period, and reduced percentage REM sleep (P < 0.01). Shortened and fragmented sleep with 60 and 100 mg were associated with reduced sleep efficiency indices (P < 0.001), and shorter sleep period times led to reduced REM/NREM ratios. Absence of an effect on REM latency for the subjects as a group may be related to relatively slow absorption. 4 The heterocyclic amphetamine derivatives have variable effects on sleep. The differences may be dose related, and wakefulness and reduced REM sleep may be seen together or separately. Alterations in sleep occur with doses of pemoline and prolintane which also modify performance.