Our objective was to investigate the role of Gardnerella vaginalis in intra-amniotic infection by use of comparative, quantitative cultures on selective media and by detection of maternal antibody response. Amniotic fluid was collected from patients with intra-amniotic infection and from matched control women. In addition to media for aerobes, anaerobes, and mycoplasmas, we used V agar-selective (Remel, Lenexa, KS) to isolate G vaginalis. Acute and convalescent maternal sera were collected and assayed for antibodies by a microenzyme-linked immunosorbent assay (ELISA) prepared against whole cells of G vaginalis. Gardnerella vaginalis was isolated in the amniotic fluid of 24 (28%) of the 86 patients with intra-amniotic infection, but this was not significantly different from the isolation rate in amniotic fluid of 86 matched controls (21%). No patient exhibited G vaginalis bacteremia. The ELISA performed on paired sera of selected patients showed that 25 had intra-amniotic infection (eight G vaginalis-positive, 17 negative), and 18 were asymptomatic (seven G vaginalis-positive, 11 negative). The amount of G vaginalis antibodies detected by ELISA in acute sera was similar in all four groups. Mean changes during convalescence were small (.053-.084 optical density units) and not significantly different. Although G vaginalis is found commonly in amniotic fluid of patients with intra-amniotic infection, the data do not support a pathogenic role for this organism; however, a facilitating role in polymicrobial infection cannot be excluded.