In this preprint, Veras et al. report a cohort study of 32 patients with critical and severe COVID-19. The authors found increased concentrations of neutrophil extracellular traps (NETs) in plasma, tracheal aspirates and lung tissue of patients and show that neutrophils from patients spontaneously released higher levels of NETs than their counterparts from healthy controls. Interestingly, in vitro experiments showed that SARS-CoV-2 can induce NET formation in neutrophils from healthy controls, with viral antigens being detected inside the cells. In co-culture experiments, these NETs induced apoptosis of lung epithelial cells. The authors suggest that inhibitors of NET synthesis or promoters of NET fragmentation may be beneficial in patients with COVID-19.