This paper summarizes the results of several fatigue studies of bus and truck drivers using different approaches. It presents findings from 24 city bus drivers obtained by the use of biochemical and psychophysiological tests before and after 7 h of driving. It presents an acoustic speech analysis conducted on 34 bus drivers before and after driving. Also, for a small group of city bus drivers, a continual examination of heart rate was carried out by electrocardiorecorder. Questionnaire studies on fatigue are related to the responses of 200 long-distance truck drivers and 107 dump-truck drivers who work in one copper mine. The last approach deals with the analysis of long-distance truck drivers' activities (driving, loading-unloading, resting and sleeping) during trips, based on their individual records. On the basis of these different approaches to bus and truck drivers' studies, clear psychophysiological, speech and subjective changes have been demonstrated and, on a descriptive level, certain symptoms observed during prolonged driving have been interpreted as effects of drivers' fatigue.