Arrowsmith, written by Nobel laureate Sinclair Lewis in collaboration with science writer Paul de Kruif and published in 1925, is devoted to one of the most important milestones in the history of modern biomedicine, namely the discovery of the ‘bacterium-eating’ virus: the bacteriophage. In various settings, and in a highly dramatic fashion, the novel reveals the basic moral ambivalence that runs through biomedicine as a research field, namely the tension between ‘pure’ research on the one hand and its (allegedly beneficial) medical applications on the other. Whereas on the ‘manifest’ level biomedicine seems intent on doing good (working for the benefit of patients), an in-depth analysis rather uncovers that there is a deeper impulse (an obsession even) at work that cannot be reduced to purely utilitarian or altruistic motives. A psychoanalytical reading of Arrowsmith allow us to discern how beneath the desire of biomedicine to do good, and to contribute to the well-being of patients, there is a deeper impulse at work, directed towards power and control over life. Indeed, biomedicine's cupido sciendi (its ‘will to know’) is fuelled by a latent ambition that may have detrimental consequences, not only for research subjects, test animals and patients, but also for the scientists themselves, as the novel sets out to demonstrate. The aim of my psychoanalytical reading is to bring this latent, disconcerting impulse, giving rise to a chronic and symptomatic moral ambivalence, to the surface.