In a context of premature rupture of the membranes, the authors compare the sensitivity and ability to predict the onset of chorio-amnionitis of the conventional clinical signs (hyperthermia, fetal tachycardia, discolored amniotic fluid) and paraclinical signs (hyperleukocytosis and bacteriology of the amniotic fluid) with those of the assay of C reacting protein in the maternal plasma. The latter test is apparently more sensitive and of greater positive predictive value in this disorder.