['To evaluate the hydrogen peroxide ability to induce the synthesis of matrix metalloproteinase-9 (MMP-9) in an in vitro chorioamniotic membrane model.', 'An experimental, transversal, analytic and prospective study was made. From amniotic membranes (n = 13) of term labour pregnant women chorionic and chorioamniotic explants were prepared; these were stimulated with hydrogen peroxide [200 mcM]. A group of explants were cultured with vitamin C, 48 hours prior to the hydrogen peroxide stimulus. Twenty-four hours after hydrogen peroxide stimulus the supernatants were collected and metalloproteinase-9 production was determined by zymography methods.', "Hydrogen peroxide induced the synthesis of metalloproteinase-9 in chorionic and chorioamniotic membranes. When chorionic and chorioamniotic membranes were cultured with vitamin C prior to the hydrogen peroxide stimulus, the MMP-9 production diminished (p < 0.05; Dunn's method)."] Does [ Vitamin C decrease MMP-9 synthesis induced by hydrogen peroxide in an in vitro chorioamniotic membrane model ]?