To investigate the correlation between chorioamnionitis and premature rupture of membranes (PROM), the influence of human recombinant interleukin-1 alpha (hrIL-1) on the metabolism of glycosaminoglycans (GAGs) and collagen in cultured human chorionic cells was examined and the following results were obtained. 1. When chorionic cells were incubated with D-[6-3H] glucosamine, the cells biosynthesized and rapidly secreted GAGs into the medium. After a 24-hr incubation, approximately 75% of total GAGs was distributed in the medium fraction, and more than 75% of these GAGs were found to be a high mol. wt (more than 1 x 10(6] hyaluronic acid. 2. hrIL-1 enhanced the biosynthesis and secretion of hyaluronic acid in a dose dependent manner, but hrIL-1 did not change the mol. wt of hyaluronic acid. In addition, no remarkable effect of hrIL-1 was exerted on the biosynthesis of the sulfated GAGs, therefore the consequential decrease in their relative concentrations was observed. 3. Collagen biosynthesized by chorionic cells increased linearly in proportion to the incubation period, and after a 12-hr incubation, about 75% of the tritilated collagen was secreted into the medium fraction. hrIL-1 did not modulate production of the collagen and noncollagenous protein in the cells. 4. hrIL-1 induced collagenase production in chorionic cells and significantly accelerated its production in a dose dependent manner, without affecting cell proliferation. The stimulatory effects of IL-1 on the biosynthesis of hyaluronic acid and collagenase are connected with the decrease in tensile strength observed in PROM. Thus, it is proposed that IL-1 from effused leukocytes in fetal membrane plays an important role in PROM with chorioamnionitis.