Quantitative and electrophoretic analysis of the rabbit's eustachian tube lavage fluid were performed by Lowry's method and sodium dodesyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE), respectively. Mean value of the quantity of protein in the eustachian tube lavage was 2.4mg/tube and the electrophoretogram of the eustachian tube lavage fluid showed three bands of protein. The calculated molecular weight of the three proteins in the eustachian tube lavage fluid was 79400, 63100 and 50100 daltons, respectively. To determine whether the three types of proteins in the eustachian tube lavage fluid originated from serum, its electrophoretogram of the eustachian tube lavage fluid originated from serum, its electrophoretogram was compared with the electrophoretogram of the serum protein. By this comparison, its was revealed that a band of protein(M.W. 50100 daltons) on the electrophoretogram of the eustachian tube lavage fluid was not identified on the electrophoretogram of the serum protein. Above results suggest that eustachian surfactant contains protein and the protein of molecular weight 50100 daltons is eustachian surfactant specific.