Squamous cell carcinoma antigen levels in 74 healthy volunteers, 57 patients with CIN and 91 patients with cervical carcinoma were determined by radioimmunoassay. 5.4% of healthy volunteers were above and all patients with CIN were below 3.0 ng/ml. 63.1% of 65 patients with primary squamous cell carcinoma, 1 out of 7 adenocarcinomas and 68.4% of 19 patients with recurrence of squamous cell carcinoma of the cervix had elevated SCC antigen levels. Elevated posttreatment levels carried a high risk factor of tumor persistence. Increases in SCC antigen levels during follow up usually signified recurrent carcinoma.