High concentrations of tumour necrosis factor may threaten the well-being of the foetus. Secretion of soluble cytokine receptors has been suggested as a mechanism for regulating cytokine activity in vivo. In this study pregnancy-related materials were examined for the presence of soluble receptors (p55 and p75) for tumour necrosis factor. In contrast to control materials, serum and urine samples from pregnant women and newborns contained high concentrations of p55, and p55 was highly expressed by villous syncytiotrophoblasts. Thus, the present data suggest that shedding of specific receptors may contribute to the regulation of tumour necrosis factor activity throughout a normal pregnancy.