A revealed-preference-based method is proposed for assessment of the environmental and human health impact of genetically engineered (GE) crops. This method employs the relative pesticide toxicity information from farmers' pesticide choices combined with volume of pesticides as an alternative to previous methods which are based on volume only, on number of pesticide applications, or on stated preferences. The method is applied to estimate the changes in the impact of herbicides after environmental and health perspective. The results indicate that, on average, a reduction in herbicide human heath and environmental impacts occurs when farmers adopt RR soybean varieties.