Cell-mediated immune response by lymphocyte induced through recognition of HBV core antigen during acute HBV infection, chronic HBV infection and in subjects recovered from HBV infection was investigated in the present study by assessing the competence of IFN-gamma secretion by cultured PBMCs on stimulation by HBV nucleocapsid antigen (HBcAg). Fresh blood was collected in heparin from acute, chronic and recovered groups of HBV infected patients and uninfected vaccinated healthy controls aged between 18-50 years. PBMCs were separated by Ficoll-Hypaque density gradient centrifugation technique and were stimulated with hepatitis B virus core antigen (HBcAg) and mitogen (lectin). Stimulated PBMCs were cultured in CO2 and IFN-gamma levels were measured from the culture supernatant by an in-house ELISA technique. The mean+/-SE levels of IFN-gamma in HBcAg stimulated PBMCs in acute, chronic, recovered and controls groups were 875 pg/ml+/-297.56, 128.50 pg/ml+/-33.66, 905 pg/ml+/-172.51 and 235.33 pg/ml+/-111.28 respectively. IFN-gamma levels produced by HBcAg stimulated PBMCs of acute and recovered groups were significantly higher than that of chronic and control group (p<0.001). All groups responded strongly to lectin stimulation. Thus, it may be concluded that patients with acute HBV infection and those who had recovered from HBV infection show vigorous response to HBcAg stimulation in contrast to patients with chronic HBV infection.