In order to understand the role of interleukin 1 (IL-1) in pregnancy, the amount of IL-1 in normal human amniotic fluid (AF) from various gestational ages and delivery was measured using an ELISA. AF samples were divided into three groups of varying gestational ages. Group 1 of AF was collected by amniocentesis from gestational ages less than 24 weeks (n = 13). Group 2 was collected transvaginally during delivery following labor greater than or equal to 36 weeks (n = 36). Group 3 was transabdominally collected from elective cesarean section without labor greater than or equal to 36 weeks (n = 8). IL-1 alpha was present in AF of early gestational age, 19.2 +/- 21.7 pg/ml, in group 1, and appeared to increase with gestational age, 63.4 +/- 50.1 pg/ml, in group 3. In contrast, IL-1 beta was not detectable in either group 1 or 3. However, the concentrations of IL-1 in group 2 was extremely high (IL-1 alpha, 233.1 +/- 351.9 pg/ml; IL-1 beta, 1,093.5 +/- 1,369.7 pg/ml) compared to the other groups. Moreover, these concentrations tended to increase with the duration of labor. IL-1 alpha and IL-1 beta concentrations in AF were intimately related. These findings suggest that IL-1 has some roles during pregnancy and especially during labor.