Viral DNA of the hepatitis B virus (GenBank accession number: V00867) digested with BamHI was cloned to pBR322. Reverse transcriptase PCR was conducted for HCV viral RNA (GenBank accession number: AB031663) from patient serum purified using a QIAmp viral RNA Mini kit (Qiagen K.K.) with the PCR primers designed to the sequence of 5' non-coding region and core. The PCR product was cloned to pBR322 according to the established method. Concentrations of the respective plasmids obtained were determined by 260-nm spectrophotometer (Ultrospec 20000, Pharmacia Biotech). The template DNA solutions for LAMP reactions were prepared by serial dilution of the plasmid solutions and purchased lambda DNA solution (Takara Bio, Inc.) with Tris-HCl buffer (10 mM, pH8.0) until it contained 1,000 copies/5 µl.