We provide evidence that transient institutional investors (i.e., those actively trading to maximize short term profits) trade to exploit the post-earnings announcement drift (PEAD). We estimate that transient institutions’ arbitrage generates an abnormal return of 5.1% (or 22% annualized) after transaction costs. In addition, their arbitrage trades accelerate the speed that stock prices reflect the implications of current earnings for future earnings. However, transient institutions trade less aggressively to exploit PEAD in firms with high transaction costs. Our results contribute to understanding the role of transient institutional investors in explaining the persistence of PEAD.