Human chorionic gonadotropin (beta-hCG) has been detected within tissue homogenates, culture fluid, and sera of patients with squamous cell carcinoma of the cervix. Studies regarding in vivo localization of beta-hCG in squamous cell carcinoma of the cervix are scant and conflicting. Cervical samplings (biopsy and/or curettage specimens) of 63 cases of poorly differentiated invasive squamous cell carcinoma of the cervix were initially stained by the immunoperoxidase technique for the presence of beta-hCG and human placental lactogen (hPL). Based on beta-hCG reactivity, patients were divided into beta-hCG-positive and beta-hCG-negative groups. Thirty-three of the 63 (52%) cases showed localization of beta-hCG in tumor cells. Subsequent specimens of patients, who underwent surgical treatment, were likewise examined for beta-hCG reactivity. These surgical specimens showed focal beta-hCG reactivity in the beta-hCG-positive group only. The beta-hCG reactivity was seen in both high-grade SIL (CIN III), invasive squamous cell carcinoma, and its metastases. The focal beta-hCG reactivity was predominantly confined to the peripheral tumor cells at the stromal-epithelial interface in noninvasive and invasive lesions. Intensity of immunostaining was moderate to strong. The beta-hCG staining was observed in different cancer stages and in various age groups. No hPL reactivity was seen in any cases. Poorly differentiated squamous cell carcinoma of uterine cervix showing immunoreactivity for beta-hCG should be distinguished from choriocarcinoma and other trophoblastic tumors.