Histatins 1 and 3, MUC5B, and human neutrophil defensins (HNPs) inhibit the infectivity of influenza A virus (IAV). Inhibition of infectivity of the Phil82 strain of IAV was tested using the fluorescent focus assay as in Fig. 1. In the left panel more abundant salivary proteins [histatins, proline-rich proteins (PRPs), amylase, and MUC5B] were preincubated with the virus and then inoculated on Madin–Darby canine kidney cells. Histatins 1 and 3 and MUC5B significantly inhibited infectivity at all the concentrations tested (P < 0.01 compared to control for all). Results are mean ± SEM of three or more experiments. PRP, amylase, and histatin 5 did not inhibit infectivity. In the right panel less abundant salivary proteins were tested. Among these only HNPs 1 and 2 inhibited infectivity.