Since pulmonary endothelial dysfunction is a hallmark of COVID-19-induced ARDS and considering that, until now, a small number of studies have reported elevated levels of ET-1 in the circulation of COVID-19 patients [31,32], in this study, we aimed to explore whether COVID-19 ARDS patients present with an imbalance between the pulmonary synthesis and clearance of ET-1. Here, EDN1 is linked to acute respiratory distress syndrome.