Trophoblastic cells abundantly express epidermal growth factor (EGF) receptors, which, when activated by EGF or transforming growth factor-alpha, can influence cellular growth and metabolism. Various lymphocyte and macrophage cytokines have been found to influence the proliferation of human choriocarcinoma (CCA) cells in vitro. In the current study we investigated the possibility that certain cytokine effects are mediated by changes in EGF receptor expression. JEG-3 human CCA cells were incubated with varying concentrations of interleukin 1-alpha (IL-1 alpha), interleukin 1-beta (IL-1 beta), interleukin 2, gamma-interferon, granulocyte-macrophage colony stimulating factor and tumor necrosis factor-alpha (TNF), and the expression of EGF receptor was measured by radioimmunoassay using a murine monoclonal antibody with specificity for the EGF receptor. Proliferative or growth suppressive effects of the cytokines were assessed by quantitative analysis of the DNA in the cell culture wells. Macrophage-derived cytokines IL-1 alpha, IL-1 beta and TNF significantly suppressed cell growth; this was associated with a significant increase in EGF receptor expression. The other cytokines had no significant effect on either EGF receptor expression or cell growth. We also studied the expression of EGF mRNA in JEG-3, Jar and BeWo CCA cell lines. By reverse transcription followed by polymerase chain reaction, low levels of EGF mRNA were detected in all three cell lines. Therefore, EGF may be synthesized by JEG-3, Jar and BeWo CCA cell lines to participate in an autocrine growth pathway. Our findings support the concept that cytokines may act as paracrine mediators of autocrine processes involved in CCA cell growth regulation by modulating growth factor receptor expression.