Recent studies have shown that periodically disrupted sleep resulted in significant daytime sleepiness and performance loss in normal young adults. One study suggested that the periodicity of disturbance rather than the total number of sleep disturbances was the primary factor in causing degraded function. However, in that study, increased performance levels could have been associated with increased levels of slow wave sleep. The present study was designed to determine whether the amount of SWS rather than the periodic disruption of sleep accounts for decreased performance of Ss with disrupted sleep. Twelve normal young adults spent two 4-night periods in the laboratory. During one 4-night series, Ss were briefly aroused either following each 10 min of sleep or whenever they entered stage 3 sleep (No SWS condition). During the second series of nights, Ss were briefly aroused after each 10 min of sleep (SWS condition). In the second series, additional arousals were performed after 5-min periods (but not when Ss were in SWS) to equalize the total number of arousals in the SWS conditions with those in the No SWS condition. Total experimental arousals were equal in the disruption conditions, and the experimental manipulation was successful in reducing total SWS to infrequent epochs of stage 3 in the No SWS condition while allowing significantly more SWS in the SWS condition. In terms of sleep stages, this difference was balanced by increased stage 2 in the No SWS condition. Despite the differential occurrence of SWS, no performance, mood, or nap latency measure was different in the SWS vs.(ABSTRACT TRUNCATED AT 250 WORDS)