We observed the immunological answer to antigens obtained from the human malignant breast tumor and from the blood of inbred mice strain C3H/H2K infected by LDH virus. We compared the modified ELISA method for humoral immunity with the leukocyte adherence inhibition (LAI) assay for cell-mediated immunity. The modified ELISA method is suitable for early diagnosing and monitoring antibodies in a malignant breast tumor simultaneously with senological examinations which include mammography and clinical examinations, because the antibodies are determined in a high number of samples by single application.