Serum concentrations of interleukin 6 (IL-6) and C-reactive protein (CRP) were determined in 74 patients with various histological types and clinical stages of breast carcinoma, recurrent breast carcinoma and of benign breast tumor. The concentrations of IL-6 and CRP were significantly increased in carcinoma patients relative to control group and to benign breast tumor group. The frequency of higher levels and absolute value of IL-6 and CRP showed tendency to significant increase with the stage of disease. A positive correlation was observed between the concentrations of IL-6 and CRP. Our results suggest that of IL-6 assay may be useful in estimation of progress disease in patients with breast carcinoma.