Abstract. Drawing on a wide array of evidence ranging from historical databases of homicide convictions to psychological laboratory studies of essay writing, we develop the hypothesis that men will behave more aggressively in salary negotiations than women and will, as a consequence, receive higher salaries, holding other influences constant. We test this hypothesis using data from the National Study of Carreers. We find that a significant difference in income remains after numerous other influences have been controlled for. This is strong evidence in favour of our hypothesis. Despite the fact that we did not measure aggressiveness in salary negotiations. At all.