Serum levels of squamous cell carcinoma antigen were measured in 688 samples from 119 patients with cervical cancer. Ninety-seven patients had primary tumors and 22 had recurrent disease. Serum samples were obtained before each cycle of chemotherapy, before surgery, at least 4 weeks after surgery, and at 2- to 3-month intervals during follow-up from 78 of the patients with locally advanced cervical cancer who were receiving neoadjuvant chemotherapy. Squamous cell carcinoma antigen serum levels were elevated (greater than 2.5 ng/ml) in 71% of the patients with primary tumors and in 77% of the patients with recurrent carcinomas. The percentage of positivity increased significantly with stage (p = 0.03) and was higher in squamous cell tumors than in adenocarcinomas (p less than 0.001). Pretreatment squamous cell carcinoma antigen levels were not predictive of neoadjuvant chemotherapy response; however, the serial measurement during chemotherapy showed a good correlation with clinical response. In the patients who had surgery, squamous cell carcinoma antigen positivity did not correlate to pathologic findings (lymph node status, cervical and parametrial infiltration). Disease-free survival was significantly longer in patients with squamous cell carcinoma antigen pretreatment values that were lower than 5 ng/ml, compared with patients with marker higher than 5 ng/ml (p less than 0.01). Abnormal squamous cell carcinoma antigen serum levels preceded the clinical detection of recurrence in eight of 11 patients with a median lead time of 5 months.