An Excretory Secretory protein antigen of 6 kDa (ES-6) was isolated from Mycobacterium tuberculosis H37Ra culture filtrate by gel filtration using fast protein liquid chromatography. Seroreactivity of ES-6 antigen was compared with earlier reported diagnostically useful ES-31 and ES-43 antigens at different stage of pulmonary tuberculosis and in household contacts of the patients. The ES-31 and ES-43 antigens showed good immune response in chronic and relapse cases respectively while ES-6 antigen has shown comparatively low immune response in these cases. However ES-6 showed in-creased seroreactivity in household contacts of pulmonary tuberculosis patients. These results suggest the heterogeneous responses of antigens in different disease conditions and immune response to ES-6 antigen may be associated with latent infection for predicting active disease in course of time, as observed in the follow up of these individuals.