Early diagnosis is the key for the successful treatment of breast cancer. A serum marker for the early detection of breast cancer could significantly reduce breast cancer morbidity and mortality by bringing the time of diagnosis at an earlier and therefore still curable stage. So far, no biomarker for the early detection is available for the clinical routine. The aim of the present study was to evaluate the use of calponin-h2 as a blood-based biomarker for the early diagnosis of this disease. Using two monoclonal antibodies against calponin-h2, we developed a sandwich ELISA to analyze the serum levels of calponin-h2. In order to evaluate the diagnostic potential of this biomarker, patients with breast cancer (n = 76), benign diseases of the breast (n = 51) and healthy females (n = 24) were analyzed. Serum levels above 10 ng/ml were only observed in patients with breast cancer (n = 8; 10.5%). Further large-scale studies and preanalytic evaluations are necessary to clarify the definite role of calponin-h2 as a biomarker in breast cancer management.