Human labor is characterized by dramatic physiological and structural alterations of the cervix and overlying fetal membranes, leading to myometrial activation and delivery. To investigate the potential mechanism of these changes, we performed 2D PAGE proteomic analysis on serial cervico-vaginal fluid samples obtained from women during late pregnancy and spontaneous labor. We identified 9 protein spots that were significantly altered ( p 0.05) in association with spontaneous term labor. Eight protein spots were definitively characterized by electrospray ion-trap mass spectrometry yielding 7 different proteins: cystatin-A, interleukin-1 receptor antagonist, glutathione S-transferase P, peroxiredoxin-2, thioredoxin, copper-zinc superoxide dismutase, and epidermal fatty-acid binding protein. These proteins are involved in protease inhibition, anti-inflammatory cytokine activity, and oxidative stress defense. These findings may provide an insight into the biochemical processes and timing associated with extracellular matrix remodelling of the cervix, supracervical fetal membranes, and myometrial activation in association with spontaneous term labor. Application of these findings may lead to development of predictive biomarkers of labor onset.