The diagnosis and treatment of fibrotic hypersensitivity pneumonitis (fHP) poses significant challenges. Its differentiation from idiopathic interstitial pneumonias can be problematic, but is important as fHP, especially the presence of fibrosis, has been associated with significant morbidity and mortality.1 The challenges posed by accurate diagnosis have been highlighted in a multicentre study demonstrating poor multidisciplinary agreement in the diagnoses of HP compared with idiopathic pulmonary fibrosis (IPF).2 A consensus-based diagnostic approach has been established,3 with the subsequent development of an international guideline providing some clarity on the diagnosis of fHP. However, several questions on the management of fHP remain, emphasising the need for clinical trials of therapies in fHP.4 Much of our clinical practice using immunosuppressant therapies stems from retrospective observational studies with limited patient numbers showing modest improvements in lung function and reductions in prednisolone therapy,5 and from one small remote randomised trial of the use of corticosteroids in HP.6 However, patients with fHP who require immunosuppressive therapies have worse survival,7 thus highlighting the urgent clinical need for additional therapeutic options in fHP, based on high quality evidence from prospective studies. …