A replica-plate assay was used to screen for the interaction of salivary molecules with dental plaque bacteria. Bacterial colonies cultured from supragingival plaque on sheep-blood (SB) agar were replica-plated onto nitrocellulose membranes overlaying SB or mitis-salivarius agar. Membranes with attached colonies were removed and incubated with 125I-amylase or 125I-proline-rich glycoprotein (PRG). Positive interactions were detected by autoradiography. Only strains of Streptococcus gordonii and Actinomyces viscosus bound amylase, and strains of A. viscosus bound PRG. The results suggest that amylase and PRG bind to selected species of aerobic dental plaque bacteria.