ABSTRACT: A total of 347 cDNA were isolated from the mantle of the oyster Crassostrea gigas by the suppression subtractive hybridization method. By northern blot analysis, we found the mRNA sequences of the several cDNA were highly expressed in the mantle. A total of 61 sequences showed close similarities to known sequences, and they were classified into seven groups: (i) protein synthesis; (ii) cytoskeleton; (iii) signal transduction; (iv) extracellular matrix; (v) metabolism; (vi) transcription factors; and (vii) others. Number 64 cDNA was more similar to the actin of Placopecten magellanicus than C. gigas, indicating that C. gigas has two isotypes of actin genes. This work is the first step to clarify functional activities of the mantle at the molecular level.