Interleukin-6 (IL-6) is a pleiotropic cytokine that is not only a mediator in major immunologic reactions but also a growth factor of keratinocytes. We studied the IL-6 secretion in vitro of 15 human cell lines derived from both squamous cell carcinoma (SCC) and adenocarcinoma of the uterine cervix. Four of the eight well differentiated SCC secreted a large amount (> 1500 pg/48 h/10(6) cells) of IL-6 in nude mice. In contrast, poorly differentiated SCC cell lines and all of the 7 adenocarcinoma cell lines secreted a small amount (< 500 pg/48 h/10(6) cells of IL-6). The expression of IL-6 mRNA of the cell lines correlated well with their IL-6 secretion potential. However, the expression of IL-6 receptor did not correlate with the IL-6 secretory potential. We also studied the IL-6 secretion of freshly isolated normal squamous epithelium and of dysplastic epithelium. In culture, two normal squamous epithelia secreted a large amount (> 2000 pg/48 h/10(6) cells), whereas 8 dysplasia epithelia secreted an extremely small amount (< 10 pg/48 h/10(6) cells). About one-third of patients with SCC had a raised serum IL-6 value. IL-6 production may help to differentiate between SCC and adenocarcinoma of the uterine cervix. IL-6 regulation seems to change in the course of SCC carcinogenesis.