Hepatitis C virus (HCV) RNA was detected in the irrigating solution aspirated by the ultrasonic dissector system used in liver surgery with a reverse transcription polymerase chain reaction technique and was then compared with HCV RNA in the serum to clarify the risk of viral transmission to hospital personnel. The positivity of HCV RNA in the aspirated irrigating solution was approximately equal in all patients whose serum was positive for HCV RNA. However, viral RNA was not detected in the aspirated irrigating solution of any patient who was seronegative for HCV RNA. These results indicate that it is necessary to be cautious regarding the transmission of HCV during liver surgery when using the ultrasonic dissector in HCV RNA seropositive patients, because the irrigating solution aspirated by this device appears to be highly infectious.