Radioimmunoassay (AlA) is generally used to measure certain salivary hormones because of its high sensitivity. For speed and simplicity, it has been used in the form of “direct” assays, i.e., without first extracting the analyte from its matrix. investigating the effect of the principal salivary proteins on the binding behavior of three commercial AlA kits, we found that the Amerlex-M [125I]progesterone binding was greatly reduced when a-amylase and mucins were added to the binding medium, whereas igA and lgG were less effective. The Serono Biodata [125I]testosterone binding was unaffected by proteins, while the Amertex [125ljcortisol binding was decreased by a-amylase and mucins. The protein influence was largely eliminated when an extraction step was incorporated. Thus, direct RIA of saliva may be subject to matrix effects, to extents that vary with the kit and that may adversely affect the quality of the assay results.