The diagnostic value of a new tumor marker, CYFRA 21-1, was studied in the sera of 50 controls, 206 patients with benign diseases and 469 patients with malignancies. Fifty controls showed mean serum concentrations of 1.2 +/- 0.5 ng/ml. Using 3.3 ng/ml as the cutoff, abnormal CYFRA levels were found in 13.1% of patients with benign diseases, mainly in those with liver cirrhosis (29.4%) or renal failure (20.8%), and in 44.4% (180/405) of patients with active cancer. Neither healthy subjects nor no evidence of disease (64 cases) patients had serum levels higher than this limit. CYFRA 21-1 results were significantly higher in patients with active cancer than in those with benign diseases or without active tumors (p < 0.0001). CYFRA serum levels were significantly higher in patients with metastases (59.5%) than in those with locoregional disease (33.7%; p < 0.001). CYFRA 21-1 sensitivity in patients with lung cancer was related to tumor histology with abnormal levels in 65.6% of patients with non-small cell lung cancer and in 25% of patients with small cell lung cancer (p < 0.0001). In breast cancer, CYFRA 21-1 concentrations were significantly higher in patients with metastases and in patients with primary tumors but with nodal involvement (p < 0.001).