In order to investigate the correlation between uterine contraction and Interleukin-6 (IL-6), we studied the effects of the prenatal course and uterine contraction on IL-6 and the soluble Interleukin-6 receptor (sIL-6R) concentration in human amniotic fluid. We also determined the effects of IL-6 on the permeability of the human amnion cell monolayer. The results were as follows: 1) The level of IL-6 at full term delivery was significantly higher than that at premature delivery. 2) The level of IL-6 without uterine contraction was significantly (p < 0.05) higher than that with uterine contraction. 3) The mean sIL-6R value at full term delivery was 1.28 +/- 0.21 ng/ml. There was no correlation between sIL-6R and the prenatal course. 4) IL-6 enhanced permeability in the human amniotic cell monolayer. This effect of Il-6 was concentration dependent and time dependent. These results show that uterine contractions increased the IL-6 concentration in human amniotic fluid, and suggest that uterine contraction enhanced the permeability of the human amniotic cell in vivo.