Serum endocan, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin were measured in “severe” (n = 27), “critically ill” (n = 17) and “critically ill on VV-ECMO” (n = 17) COVID-19 patients at admission, days 3–4, 5–8 and weekly thereafter, and in controls (n = 23) at a single time point. The gene discussed is SELE; the disease is COVID-19.