Urinary trypsin inhibitor-related substance (UTI-R) was measured in the amniotic fluid (n = 30), first neonatal urine (n = 10), meconium (n = 10), and adult urine (n = 10). The concentration of UTI-R excreted in the neonatal urine was significantly higher than in adult urine and meconium. Positive immunostaining for UTI was observed in amnion, umbilical cord and placenta. The effect of UTI was studied on the amnion using fura-2-acetoxymethyl ester. Interleukin-1β (IL-1β) and tumor necrosis factor-β (TNF-β) led to a significant increase in relative fluorescence release (RFR) of fura-2 (p < 0.05 and p < 0.02, respectively) while endotoxin did not show significant changes of RFR of fura-2. The effect of IL-1β and TNF-β was almost abolished after incubation of UTI with the amnion cells (p < 0.03). This suggests that UTI may have a protective effect on the amnion especially against IL· 1β and TNF-β.