Abstract: By isolating a so far unknown novel hepatitis virus and determining the gene sequence thereof, genes, polynucleotides, polypeptides, methods for isolating virus particles, virus particles, and antiviral antibodies, which can be used for diagnosis and treatment, as well as methods for detecting viruses are provided. Disclosed is a non-B, non-C, non-G hepatitis virus gene having a nucleotide sequence from which a sequence having a length of from about 3500 nucleotides to about 4000 nucleotides can be amplified by PCR utilizing an oligonucleotide having the nucleotide sequence shown in SEQ ID NO: 57 and an oligonucleotide having the nucleotide sequence shown in SEQ ID NO: 60 as primers, or PCR utilizing an oligonucleotide having the nucleotide sequence shown in SEQ ID NO: 57 and an oligonucleotide having the nucleotide sequence shown in SEQ ID NO: 61 as primers. Based on the nucleotide sequence of the gene, polypeptides etc. are provided.