This paper provides the results of an applied research of forests engineers connected to their risk of mental stress occurrence in everyday work. This paper also has a component of a basic research, in which the adequacy and reliability of applied methodology in this kind of researches is examined. The mental stress induced risk is tested by usage of an e-mail survey which consists out of 23-part ERI (Effort-Reward Imbalance) questionnaire. For the assessment of mental stress exposure level following indicators have been used: 1) ERI--ratio of devoted effort and achieved reward, and 2) overcommitment. These indicators have been analyzed in comparison to the demographic parameters (gender, age) and the complexity of assigned jobs of the interviewees. The interview was applied on a randomly sampled forestry experts employed in public and private sector. The analysis of reliability of the three components of ERI questionnaire has showed satisfactory internal consistency. Descriptive statistics has been done regarding gender and the complexity of assigned jobs. The testing of the "devoted effort/achieved reward" variable (E/R index) has shown a statistically significant difference of the index value between male interviewees on managerial and standard expert positions. The value of E/R index was x > or = 1 at 18.97% of the sampled interviewees, which indicates a divergence between devoted effort and achieved reward, and also points to a possibility of mental stress occurrence risk. Multiple response tables have shown that female interviewees with less than 20 years of professional experience manifest stress related symptoms earlier than their male colleagues with similar professional experience do. Regression analysis has shown a significant correlation of E/R index to gender, internship and overcommitment. This research also assesses the viability of the applied method as an instrument of forestry experts' mental stress level determination.