Discrimination against women has been alleged in hiring practices for many occupations, but it is extremely difficult to demonstrate sex-biased hiring. A change  　 the way symphony orchestras  　 musicians provides an unusual way to test for sex-biased hiring. To overcome possible biases in hiring, most orchestras  　 their audition policies in the 1970s and 1980s. A major change involved the use of blind' auditions with a screen' to  　 the identity of the candidate from the jury. Female musicians in the top five symphony orchestras in the United States were less than 5% of all players in 1970 but are 25% today. We ask whether women were more likely to be advanced and/or hired with the use of blind' auditions. Using data from actual auditions in an   fixed-effects framework, we find that the screen  　 by 50% the probability a woman will be  　 out of certain preliminary rounds. The screen also enhances, by several fold, the likelihood a female contestant will be the winner in the final round. Using data on orchestra personnel, the switch to blind' auditions can explain between 30% and 55% of the increase in the proportion female among new hires and between 25% and 46% of the increase in the percentage female in the orchestras since 1970.