The value of squamous cell carcinoma antigen in patients with locally advanced cervical cancer undergoing neoadjuvant chemotherapy. 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. 