The aim of the investigation was to follow the time-of-day variations of some circadian and stress indicators during fast rotating 12-hour shifts. The study covered twenty-one male operators in thermoelectric power plant aged 35.7 ± 8.5 years. The time-of-day variations of 6-sulphathoxymelatonin (aMT6s), the main melatonin metabolite, 11-oxycorticosteroids (11-OCS), catecholamines and oral temperature were followed during the 2 nd day shift and two consecutive night shifts. The aMT6s was determined by RIA and the 11-OCS and catecholamines by fluoriphotometric methods. Moderate general activation and daily oriented circadian rhythms of aMT6s, 11-OCS and oral temperature were found in the investigated operators. The night shiftwork showed significant impact on melatonin peak values at fast rotating 12-hour shiftwork.

        Key words: 12-hour shifts, adjustment, melatonin, 11-OCS, catecholamines