Studies are carried out on 51 workers from the state works "D. Dimov"--Yambol on the changes of the pulse variability in the course of 12-hour day and night shift work and subjective evaluation of the psychosomatic complaints, in view of assessment the work load and strain. This investigation is performed because the workers have lodged a complaint against the introduction of 12-hour shift regime of work. It is done twice--during the day and during the night shift. No changes giving indication for considerable over pressure of the physiological systems and decrease of the working capacity have been established during the working process. The conclusion is that this type of working activity--12-hour shift schedule endangers neither the health status of the workers, nor the security and reliability of the system "man-machine-environment" therefore its introduction is not in contradiction to the physiologically well-grounded norms for the organization of the working process.