Background: Hepatitis B virus infection in patients who lack detectable hepatitis B surface antigen (HBsAg) is called occult hepatitis B infection (OHB). The very low level of HBV genome may hamper its detection by molecular techniques. Recently, a highly sensitive EIA utilizing a novel modified electron spin resonance (ESR) technique (modified ESR-EIA) was developed to detect HBsAg by measuring stabilized nitroxide radicals. Aim: to detect occult HBV infection, using ESR-EIA among HCV-related chronic liver disease (CLD) Egyptian patients who were seronegative for HBsAg by standard EIA. Methods: The study was conducted on two periods of time; in 1st period, 72 inpatients in Tropical Medicine Department of TBRI, were enrolled in the study. They were divided into two groups; 44 seropositive anti-HCV patients (Group I), 28 seronegative anti-HCV patients (Group II). Sera were subjected to virological assays for HBsAg, HBeAg, anti-HBc IgM, anti-HBc IgG, anti-HBs, anti-HCV and HCV RNA. We also examined serum HBV DNA by polymerase chain reaction (PCR) technique and real-time detection polymerase chain reaction (RTD-PCR). In the 2nd period; modified ESR-EIA was applied on 32 TBRI inpatients, 23 in Tropical Medicine Department (Group I) and 9 from hemodialysis unit (Group II) with HCV-related CLD. Results: OHB was detected in 18.1% and 86.9% of our patients in 2002 and 2006 respectively. In phase 1, there was a higher detection rate among HCV patients in Group I (25%) than Group II (7%), with higher prevalence (52.4%) in patients with positive HCV RNA in Group I versus those with negative HCV viremia (8%) in Group II. HBV DNA by either PCR or RTD-PCR was negative in all patients of both groups as the HBV viral load of the samples were below detectable level of the methods used; less than 100 copies/ml. None of 9 hemodialysis patients were positive for OHB. Conclusion: The newly developed quantitative ESR-EIA technique represents a great evolution for screening and diagnosing OHB in patients with CLD who are negative for conventional HBV-related serological markers. Moreover, investigation of chronic infection with a low HBV load and its clinical significance is considered to make a significant contribution to prevention and treatment. Detection of OHB would limit its nosocomial spread particularly in hemodialysis units and liver transplant recipients.