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Notes: Summary Active specific immunization with autologous irradiated tumor cells (AITC) admixed with BCG was attempted in 49 stage III breast cancer patients whose median follow-up at present is 3 years. As a first immunizing procedure 41 patients received repeated intradermal inoculations and 8 had a single endolymphatic instillation (ELI). Skin response (SR) to AITC alone was induced after two to nine weekly immunizations. Eight of 41 patients with negative or weak responses were effectively reimmunized by ELI, as indicated by conversion and invigoration of SR. Following immunization, radiotherapy to breast and axilla was administered. Thereafter, fortnightly 5-FU and monthly boosters of AITC-BCG mixture were given for 2 years. Strength of response to AITC induced by active immunization was found to relate to subsequent disease recurrence, with 15% relapsing among the good responders and 53% among the weak and non-responders. Positive SR to AITC — once elicited — was steadily maintained in the majority of patients; its decline was associated with manifest disease recurrence. Conversion to AITC positivity in vivo following specific immunization was not detectable by the LMI assay. Lymphocyte stimulation (MLTI) by AITC in vitro was found in only 9 of 26 tested patients with positive in vivo SR to AITC. Cutaneous response to AITC appears to be the only parameter of antitumor response showing clinical correlation, while specific in vitro correlates of cell-mediated immunity were found unsuitable for monitoring patients undergoing specific immunotherapy. While in vivo PPD response was mainly unchanged or enhanced, in vitro lymphocyte stimulation by PPD and PHA showed a distinct decline at the time of relapse. The cumulative proportion of relapse among the immunotherapy patients at 3 years was 32% with mortality of 12% (13 relapsed, 5 died), both being significantly lower than reported results in stage III breast cancer without immunotherapy. It is concluded that specific immunization with AITC is feasible in most breast cancer patients with loco-regionally advanced disease and that this intervention is conducive to favorable modification of the course of their disease.