We identified high serum CXCL9 levels in samples from patients with acute COVID-19 infections (n = 57), chronic bird-related hypersensitivity pneumonitis (n = 61), asthma (n = 194), and ILDs (n = 84) compared to healthy individuals (< 39.0 pg/mL). Here, CXCL9 is linked to hypersensitivity pneumonitis.