Two otherwise healthy pregnant women presented with intrauterine fetal demise and underwent unremarkable induction of labor. Histopathologic examination of both placentas revealed polarizable foreign material with minimal associated tissue reaction in the membranes and adjacent maternal decidua. No overt foreign body giant cell reaction or inflammation was seen, suggesting recent introduction of the material. Further review of the histories showed that both women had undergone cervical ripening with laminaria. These are strips of collagenous seaweed placed in a closed cervix, where they absorb moisture and swell, dilating the cervix and hastening the onset of labor. Microscopic examination and polarization of known laminaria fragments identified this substance as the likely source of the polarizable material within the placental membranes. Laminaria fragments should be distinguished from other polarizable materials such as talc, suture, and retained foreign bodies on the basis of their histologic appearance and the acute nature of the accompanying tissue reaction.