Four shiftworkers of a large oil refinery were studied with respect to sleep behavior when schedules were abruptly changed. The knowledge acquired from laboratory studies does not seem sufficient to explain sleep evolution during the days which follow the inversion. Immediately after inversion, the first day sleep is short with little paradoxical sleep (PS) and slow wave sleep, (stage 3+4 SWS), because of the poor quality at the beginning. During the following days, a tendency towards recovery is seen for sleep: it is a little longer; PS and SWS proportion increase. But sleep behavior depends strongly on individuals. Some adjust quickly their amounts of sleep, PS and SWS. In contrast, it seems that the sleep of some other subjects gets worse. There is no clearcut correlation between individual behavior and the evolution after inversion of parameters like body temperature, urinary K or VMA. With the present state of knowledge, it is very difficult to have easily obtainable indices which would allow us to estimate to what extent an individual is going to adjust after an abrupt schedule inversion.