<span style="font-size:10.0pt; font-family:"Arial","sans-serif"">We analyze the doping behavior of heterogeneous athletes in an environment of private information. In a n-player strategic game, modeled as an all-pay auction, each athlete has private information about his actual physical ability and choses the amount of performance-enhancing drugs. The use of doping substances is costly but not further regulated. The main finding of the analysis is the existence of a doping threshold. In our leading case only strong athletes dope. The level of the doping threshold is increasing in the doping costs and decreasing in the prize level. Furthermore, increasing the number of athletes affects the doping decision in two ways. More competition increases the incentives to dope for strong athletes. At the same time, we find a discouragement effect for weak athletes.</span>
