Matsuyama et al. identified the commercially available serine protease inhibitor camostat (18; Figure 8) to be a SARS‐CoV‐1 inhibitor, blocking TMPRSS2 activity at 10 µM. However, at a higher concentration (100 µM), inhibition of viral entry via SARS‐CoV‐1 S protein‐mediated cell fusion never exceeded 65% (inhibition efficiency), indicating that 35% of entry events take place via the endosomal cathepsin pathway. Interestingly, treatment with a combination of EST (a cathepsin inhibitor) and 18 resulted in remarkably blocked infection (>95%) activity of pseudotyped viruses. 109