The aim of this study was to test a possible countermeasure to jet lag: letting air crew retain their home-base sleep/wake pattern during layover. Instead of their usual adoption of local sleep hours, 19 flight attendants were scheduled to a westward layover (50 h) flight (Copenhagen-Los Angeles, -9 h) on two occasions. On one trip, crews adopted the local sleep pattern, and on the other trip, the crew retained home-base sleep hours. Subjects were monitored for 10 days before, during, and after the flight; they wore activity loggers and gave ratings through sleep/wake diaries and a questionnaire. Ratings of jet lag symptoms and sleepiness were greatly reduced during layover, but not at home, for the home-base condition. It was also found that jet lag feelings seemed to be related mainly to mean sleepiness ratings (multiple regression; 16%, beta = 0.46) and to the number of awakenings (6%, beta = 0.29) during sleep. It is concluded that retaining the home-base sleep pattern may reduce jet lag during layover.