In the first half of the nineteenth century, many Americans visited phrenological practitioners. Some clients were true believers, who consulted phrenology to choose an occupation, select a marriage partner and raise children. But, as this article demonstrates, many others consumed phrenology as an ‘experiment’, testing its validity as they engaged its practice. Consumers of ‘practical phrenology’ subjected themselves to examinations often to test the phrenologist and his practice against their own knowledge of themselves. They also tested whether phrenology was true, according to their own beliefs about race and gender. While historians have examined phrenology as a theory of the mind, we know less about its ‘users’ and how gender, race and class structured their engagement. Based on extensive archival research with letters and diaries, memoirs and marginalia, as well as phrenological readings, this study reveals how a continuum of belief existed around phrenology, from total advocacy to absolute denunciation, with lots of room for acceptance and rejection in between. Phrenologists’ notebooks and tools of salesmanship also show how an experimental environment emerged where phrenologists themselves embraced a culture of testing. In an era of what Katherine Pandora has described as ‘epistemological contests’, audiences confronted new museums, performances and theatres of natural knowledge and judged their validity. This was also true for phrenology, which benefited from a culture of contested authority. As this article reveals, curiosity, experimentation and even scepticism among users actually helped keep phrenology alive for decades.