A survey was performed on electronics workers with regard to the time - budget differences between permanent day shifts and permanent night shifts in the compressed workweek system. The collection of time - budget data was done in July 1985 and in February 1986. Of the 114 workers in the first survey, 13 were working a 3 night -4 off system (N3O4,), 22 a 3 day - 4 off system (D3O4) 15 a 4 night - 3 off system (N4O3)and 9 a 4 day - 3 off system(D4O3) . In the second survey, 21 of the 79 workers working a N3O4, system, 19 a D3O4 system, 12 a N4O3 system and 6 a 1340, system. (e.g. The N3O4 work system consisted of 3 consecutive night shifts of 12 hours each day and 4 consecutive off duty days.) Both the night workers and the day workers had a longer sleep time during the off - duty period than the shift work period. The differences of sleep time between the duty and the off - duty days, howerver, were larger for the night workers than for the day workers. On the straight off - duty days, the night workers had a 10 or more hours of night sleep, while they had a 7 or less hours of daytime sleep on the night shift days. On the last day of night shift, the workeres limited their daytime sleep and delayed their main sleep period to a usual night sleep period. As a result of this sleep phase adjustment, the night workers lost one of main sleep period, and therefore the workers in both the N3O4 and the N4O3 systems had only 6 main sleep periods. A little sleep debt was estimated from the total sleep time of the night workers in a week, while the day workers had a 56 or more hours of sleep in a week. The accumulation of sleep debt could be inferred in the permanent night work system. Because of this, the consecutive night shifts should be shortened, and especially the N4O3 shifts should be avoided for the workers health.