Globally, fraud has been rising sharply over the last decade, with current estimates placing financial losses at greater than $3.7 trillion dollars annually. Unfortunately, fraud prevention has been stymied by lack of a clear and comprehensive understanding of its underlying causes and mechanisms. In this paper, we focus on an important but neglected topic – the biological antecedents and consequences of unethical conduct – using salivary collection of hormones (testosterone and cortisol). We hypothesized that pre-performance cortisol would interact with pre-performance levels of testosterone to regulate cheating behavior in two studies. Further, based on the previously untested cheating-as-stress-reduction hypothesis, we predicted a dose-response relationship between cheating and reductions in cortisol and negative affect. Taken together, this research marks the first foray into the possibility that endocrine system activity plays an important role in the regulation of unethical behavior.