We measured soluble CD8 ((S)CD8) and microglobulin (beta-2M) in 128 breast cancer patients and in 200 controls by the ELISA method. Patient groups were: Group A-new patients; Group B-patients on follow-up; Group C-patients with metastases. The mean (S)CD8 and beta-2M were significantly higher in patients than in controls ((S)CD8 p<0.01, beta-2M p<0.0001). Both for (S)CD8 and beta-2M, groups A and C had high levels which differed significantly from Group B ((S)CD8 p<0.04; beta-2M p<0.0001). A significant correlation between (S)CD8 and B-2M was observed (r=0.379: p=0.0001). Twenty patients relapsed. In 14/20 (70%) an initial high (S)CD8 and in 10/20 (50%), high beta-2M was observed. High initial CD8 and beta-2M were able to identify 80% of relapsed patients. High (S)CD8 and beta-2M levels are indicative of tumor bulk and are able to identify patients at.