This article reports the results of an 18-month study of immune system and psychological changes in stage 1 breast cancer patients provided with relaxation, guided imagery, and biofeedback training. Thirteen lymph node negative patients who had recovered from a modified radical mastectomy were randomly assigned to either an immediate treatment or a delayed treatment control group. Multiple pre-post psychological measures were performed. Significant effects were found in natural killer cell (NK) activity (p < .017), mixed lymphocyte responsiveness (MLR) (p < .001), concanavalin A (Con-A) responsiveness (p < .001), and the number of peripheral blood lymphocytes (PBL) (p < .01). No significant psychological changes were detected; however, reductions were seen in psychological inventory scales measuring anxiety. The results show that behavioral interventions can be correlated with immune system measures, thereby replicating the results of an earlier pilot study from our Center. Discussion is provided on differential T-cell and B-cell responsiveness to behavioral interventions.