OBJECTIVE: Workload is known to affect the hypothalamus-pituitary-adrenal axis. Although many studies had revealed that job stress related factors could affect the neuroendocrine system among blue-collar workers, these studies had limitations as they had not evaluated the workload by objective methods which took into consideration individual physiological differences. This study was conducted to evaluate the effects of physical workload adjusted job stress on cortisol regulation by using objective tools for workers having various job tasks. METHODS: Among 110 foundry workers, shipyard workers, and fine machine assemblers for whom saliva samples were obtained, 102 without any past history of conditions that could affect hormonal regulation such as diabetes, and hypertension were included in this study. Among the 102 study participants, 15 workers whose saliva for morning or afternoon or heart rate monitoring data was not attained were excluded from the final analysis. Workload was evaluated by RHR (relative heart rate) using a heart rate monitor, and job stress was evaluated by Karasek's Job Content Questionnaire. Saliva samples were gathered during 8 - 9 am and 5 - 6 pm, and salivary cortisol levels were analysed by radioimmunoassay. RESULTS: After adjusting several variables which could effect cortisol secretion including job stress, among the higher RHR group morning salivary cortisol level was increased (beta=60.32, S.E.=26.35, p=0.0266), afternoon salivary cortisol level was decreased (beta=-7.43, S.E.=29.73, p=0.8044), and salivary cortisol level difference between morning and afternoon was increased (beta=72.10, SE=35.50, p=0.0509). CONCLUSIONS: As physical workload increases morning cortisol level, which is caused by the effect of arousal, and decreases afternoon cortisol level, which is caused by exhaustion, physical workload enlarges the width of diurnal cortisol variance. Therefore, physical exhaustion due to excessive workload could have adverse effects on the neuroendocrine system.