Influence of infection induced by hepatitis B virus (BHV) on the forecast of stage 3 breast cancer in 65 patients was studied. All the patients received the treatment by the scheme ''preoperative radiotherapy (RT) + radical mastectomy + postoperative polychemotherapy''. Immunoenzymatic method was used for serologic examination. Indices of 3-, 4- and 5-year survival rates indicate on delayed treatment results. The results received showed unfavour able influence BHV on delayed treatment results of patients with stage 3 breast cancer.