Partial amino acid sequences of the actinoporins Or-A (136 aa) and Or-G (144 aa) isolated from the Sea of Japan sea anemone Oulactis orientalis were determined by sequencing the clones obtained by the amplification of genomic DNA and cDNA with specific primers to the N-terminal regions of the 0. orientalis actinoporin sequences and to the C-terminal region, which is known to be highly conservative in all the known actinoporin sequences. The complete structures of Or-A (165 aa) and Or-G (173 aa) were established by sequencing the cDNA clones obtained by the fast amplification of 3'-ends of cDNA. A comparative analysis of the amino acid sequences of the Oulactis actinoporins with those of actinoporins from tropical species revealed considerable differences in the structures of their N-terminal fragments and their membrane-binding sites. We believe that these differences could explain lower hemolytic activities of Or-A and Or-G than that of actinoporins from the tropical species.