An investigation was carried out to study the effect of mechanized agricultural work on the excretion of some corticosteroids and catecholamines in tractor-drivers during a seasonal field work. Group 1 (15 subjects) was examined three times: in the morning hours before starting work and at two intervals during the first and second half of the working day. In group two (11 subjects) the characteristics of the circadian rhythm for 24h were investigated in urine collected at six intervals. The results from both studies disclose a considerable increase of the total 17-ketosteroids, total 17-oxycorticosteroids, free 11-oxycorticosteroids, nor-adrenaline and adrenaline excretion levels which indicates overactivity of the hypothalamic-pituitary-adrenal and sympathetic nervous systems. The circadian rhythms of the examined parameters are characterized by an increasing of the mesors and a lowering of the amplitudes of the rhythmic variations. No significant changes of corticosteroids and catecholamines are established. Considerable interindividual differences in the course of excretion of the studies indices as well as the lack of marked circadian rhythm in about 50% of the subjects are found.