Hepatitis C virus and hepatitis D virus have been shown to suppress HBsAg synthesis. Thus it is possible that HDV infection occurs despite the lack of detectable HBsAg. The aim of our study was to (a) determine the prevalence of HDV infection in patients with chronic hepatitis C (b) compare it with the prevalence of HDV infection in HBsAg positive patients with hepatitis B. The study group consisted of 51 chronic hepatitis C patients, 30 HIV infected drug addicts (27 of them were also positive for anti-HCV) and 102 hepatitis B patients. The participants were tested for anti-HDV, anti-HCV and HBsAg. All anti-HCV positive patients were negative for anti-HDV. Four individuals with anti-HDV belonged to hepatitis B group and constituted 3.9% of all HBsAg positive subjects. We conclude that (a) there is currently no evidence of HDV infection among HCV infected patients in our region (b) hepatitis delta infection is rare in north-eastern Poland.