In this cross sectional s tudy carried out in s pring and s ummer, 79 farmers working in different job pos itions including agriculture, hus bandry and horticulture in north of Iran were participa ted. Evaluation of the heat s tres s was conducted us ing Wet Bulb Glob Temperature (WBGT) index according ISO7243 and heat s train evaluation us ing meas uring the individual phys iological res pons es including aural, oral and mean s kin temperatures according ISO 9886. The demographic characteris tics of the s ubjects s uch as age, job experience, BMI and body area were als o gathered through a ques tionnaire. In general, the s ubjects were in middle ages (38.44±8.86 yr) and mean and s tandard deviation of years of expe rience were almos t high (17.49±9.41 yr), too. The s tatis tical analys is was performed by SPSS 18 s oftware. The res ults s howed that the WBGT index values had ranging from 24 to 32.6°C in s ummer regardles s of clothing ins ulation, metabolic rate and work res t regimens . Of cours e, by correction of thes e parameters the WBGT will accompany with an incens ement. Convers ely, the heat s train monitoring revealed that in no cas e the aural and oral temperatures are higher than the limit allowed. The bes t correlation coefficient was obtained for aural temperature and WBGT index (r= 0.84, P< 0.001). It s eems that evaluation of hot and humid environment us ing WBGT index can be as s ociated with an overes timation and encountered our judgment about the environmental condition with a s ignificant error.