Rivalta reaction is still used as a puncture fluid test for differentiation of exudate and transudate. However, the test method of Rivalta reaction has not been standardized, or positive precipitates for the reaction have not been investigated. Thus, we clarified the measurement method, and investigated Rivalta reaction-positive proteins. Rivalta reaction-positive punctuates converted to negative when pH increased to 4.6 or higher, showing the necessity of pH adjustment of acetic acid solution to 3.6-4.2 in Rivalta reaction. Using pH 4.0 acetic acid solution, 8 types of proteins were identified in Rivalta reaction-positive turbid precipitates: C-reactive protein (CRP), alpha1-antitrypsin (alpha1-AT), alpha1-acid glycoprotein (alpha1-AG), haptoglobin (Hp), transferrin (Tf), ceruloplasmin (Cp), fibrinogen (Fg), and hemopexin (Hpx). Since these are acute reactive proteins, or proteins increased in malignant tumors and infections, positivity for Rivalta reaction at the specified pH may suggest pathological inflammation.