ObjectivesWe aimed to explore the acceptance and opinions of general practitioners (GPs) on the use of procalcitonin point-of-care and lung ultrasonography for managing patients with lower respiratory tract infections in primary care. We suppose that there are several factors that can influence the physician’s antibiotic prescribing decision, and the implementation of a new tool will only be possible when it can be inserted into the physician’s daily practice, helping him/her in the decision-making process.DesignSemistructured interviews; data analysis using the grounded theory method.SettingLausanne, Switzerland.Participants12 GPs who participated in the randomised clinical trial UltraPro, which evaluated the impact of the use of procalcitonin only or an algorithm combining procalcitonin and lung ultrasonography on antibiotic prescription.ResultsGPs had mostly positive attitudes towards the use of point-of-care procalcitonin in lower respiratory tract infections and uncertainties regarding the usefulness of ultrasonography. Physicians’ prescribing decisions result from interactions between three kinds of TrustS (core category): ‘self-confidence’, ‘trust in the results’ and ‘trust in the doctor–patient relationship’. Procalcitonin reinforced the three levels of trust, while ultrasonography only strengthened the physician–patient relationship. To facilitate implementation of procalcitonin, physicians pointed out the need of coverage by insurance and of clear guidelines describing the targeted patient population.ConclusionsOur data show that there is a preference for the implementation of procalcitonin rather than lung ultrasonography for the management of patients with lower respiratory tract infections in primary care. Coverage by insurance plans and updated guidelines are prerequisite to the successful implementation of procalcitonin testing in primary care.Trial Registration numberNCT03191071