Background and aim of the work: Elevation of liver transaminases is the marker of hepatocyte affection by an inflammatory process. HCV infection is a common infection in Egypt. HCV antibodies are detected at least 6 weeks from the onset of infection; a period of time which is called window or preseroconversion phase. Moreover, the immune system is so weak as to mount for a detectable level of HCV antibodies as in cases of HIV, lymphomas and patients on chemotherapy. The aim of the present work is to study HCV core antigen as a marker of HCV infection in HCV antibody negative patients with asymptomatic elevation of liver transaminases of unknown etiology. Patients and Methods: 110 asymptomatic patients with elevated liver transaminases of unknown etiology were included in the study; 55 of them were HCV antibody negative and 55 were HCV antibody positive. HCV core antigen and HCV RNA PCR were determined in all patients. HCV antibody testing was repeated in all HCV antibody negative patients after 6 weeks. Results: Out of 55 HCV antibody negative patients with elevated liver transaminases of unknown etiology, 5 turned out to have HCV infection as proved by HCV RNA PCR. 4 of these 5 were positive for HCV core antigen. 3 of these 5 converted to HCV antibody positive after 6 weeks of follow up. Conclusion: HCV core antigen is a good marker for detection of HCV infection in HCV antibody negative patients with asymptomatic elevation of liver transaminases of unknown etiology.