Aim and objectives :-The aim of the study was to evaluate the relationship between exposure to heat (stressful stimuli) and indicators of autonomic functions in workers of thermal power station. Material and method :-133 male workers were selected out of whom 65 workers were exposed to heat (400C to 450C) emitted by boiler in boiler section for 8 hrs daily and 6 days in a week for estimation of plasma catecholamines and blood pressure. The control group consists of office workers and staff who were not exposed to extreme heat. Depending on age, they were divided into four groups. Estimation of plasma adrenaline and nor-adrenaline was carried out by HPLC method with flurimetre detection and blood pressure by mercury sphygmomanometer between cases and controls to observe the effect of heat stress on autonomic functions. Results:- It was observed that there is highly significant increase in plasma level of the adrenaline and nor-adrenaline in workers. Systolic and diastolic blood pressure raised significantly in workers. Conclusion :-The general hypothesis to emerge is that automatically mediated cardiovascular reactions to stressful stimuli (heat) may initiate progression towards sustained hypertension and coronary heart disease (CHD) in susceptible individuals