Several proteins from nacre of the oyster Pinctada maxima and the abalone Haliotis tuberculata were extracted and partly characterized. Proteins dispersed in aragonite were solubilized during demineralization with acetic acid whereas proteins adsorbed on conchiolin were extracted with sodium dodecyl sulfate and beta-mercaptoethanol. The matrix of Pinctada maxima nacre is composed of one main protein with an apparent molecular weight of 20 kDa (p20). This protein was found in the acetic acid soluble fraction of nacre, as well as in the Laemmli-solubilized extract of conchiolin. In addition, the p20 solubilized with acetic acid can form oligomers made of 6 monomers linked together by disulfide bridges. The first N-terminal 21 amino acids of p20 were determined and no homology with known proteins was found. In Haliotis tuberculata nacre, 5 main proteins were solubilized during demineralization and 3 glycoproteins were detected. Stains-all and Alcian blue staining revealed polyanionic proteins in the extracts isolated from Pinctada maxima and Haliotis tuberculata nacre.