Squamous cell carcinoma antigen (TA-4) in penile carcinoma. TA-4 antigen, originally isolated from women with squamous cell carcinoma of the cervix, is elevated in the sera of patients with squamous cell carcinomas of several sites, including esophagus, lungs, and head and neck. In this study, we compared the serum levels of TA-4 in normal volunteers, patients with resected penile squamous cell carcinoma, and patients with metastatic penile squamous cell carcinoma. TA-4 values were elevated in 5 of 11 patients (45%) who had metastatic disease. In 2, TA-4 was normal the first time metastasis was clinically detected but rose as the disease progressed. Moreover, in 3 patients in whom serial determinations were made, serum TA-4 values correlated well with disease progression and response to treatment. We conclude that TA-4 values are elevated in some patients with metastatic squamous cell carcinoma of the penis and may become a useful marker for monitoring response to therapy. 