Corroboration of SARS-CoV-2 seropositivity in dog samples with adsorption assays, the Netherlands. ELISA reactivities of the 2 positive dog samples were determined against SARS-CoV-2 S1, RBD, and BCoV S1 after mock adsorption or adsorption with HCoV-229E S1, SARS-CoV-2 S1, or BCoV S1 proteins. The 2 seropositive dog samples (027 and 2H5) are from the SARS-CoV-2–exposed cohort and 2020 cohort, respectively BCoV, bovine coronavirus; HCoV, human coronavirus; RBD, receptor-binding domain; S1, spike protein subunit 1; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.