The study examined lymphokine-activated killer cell (LAK) and natural killer (NK) cell activity in breast cancer patients prior to surgery as compared to effector cell lysis in patients with non-malignant breast tumors, further in connection with lifetime diagnosis of major depression, severity of current depression, anxiety and coping styles. Follow up studies covered a period of 6 and 12 months. Prior to surgery, life time diagnosis of major depressive disorder, trait anxiety and coping styles did not discriminate patients as far as effector cell lysis is concerned. LAK activity but not NK activity was reduced in patients with actual depressive symptoms (P < 0.01) and high state anxiety (P < 0.05). These findings support the hypothesis that LAK activity is a state marker of actually existing depression and anxiety prior to surgery. Affective rather than coping measures showed significant differences in LAK activity. For LAK activity, 1 year after surgery the only predicting factors were Tamoxifen therapy and chemotherapy.