Writing in Nations’ Business in 1939, Doncaster Humm marketed his recently published psychological test, the Humm-Wadsworth Temperament Scale (HWTS), as a scientific tool that would help businesses select the right person for the right job. Through questions ranging from ‘Do you like movie heroes?’ to ‘Is a disappointment more likely to make you angry than sad?’, the HWTS promised to screen out problem employees and select for talented employees. Between its initial publication in 1935 and World War II, over two million people took the test, most often through workplace personnel departments in companies like Lockheed Martin and Western Electric. What can account for the HWTS’s initial popularity, at a time when many psychological tests were met by industry skepticism? What was it about temperament that appealed to management? And why should anyone care about an old obsolete psychological test? I argue that crucial to the HWTS’s success were Humm and his co-author Guy Wadsworth’s aggressive marketing strategies, bolstered by their respective scientific and corporate credentials, and a hospitable corporate climate. Both Humm and Wadsworth actively tried to shape the scholarly, business, and popular debate around the test, publishing in journals of academic and applied psychology, personnel journals, and popular newspapers and magazines. The backgrounds of Humm, a psychologist who had researched the heritability of mental disorders, and Wadsworth, a corporate vice-president of personnel, allowed them to ground the test’s claims in both scientific knowledge of temperament and management talk of efficiency and productivity. The test’s adoption was deeply rooted in the context of American labor relations of the 1930s, which saw increasing strife between management and labor. Since the 1935 Labor Relations Act, management was prohibited from directly asking employees about union sympathies and using that information as basis for personnel decisions. The HWTS’s claims to screen out maladjusted workers was a persuasive marketing strategy, as both psychologists and business executives equated maladjusted workers with union agitators, socialists, and political radicals. The HWTS remains little known by psychologists, historians of science, and the general public. But as I will argue, the test’s development, focus on temperament and use by management reflect an important part of the history of applied psychology and labor relations in America.