Serum levels of C‐reactive protein (CRP), white blood cell count (WBC), amniotic fluid white blood cells (Gram staining) and leukocyte esterase (LE) activity were measured serially and prospectivelq in 30 pregnant women in labor at term. Results were retrospectively compared with amniotic fluid bacterial culture results. Leukocyte esterase activity was measured by the dipstick test (Nephurtest) and anin vitrophotometric method. Amniotic fluid samples were collected through an intrauterine transvaginal pressure catheter. The serial CRP and WBC levels from admission to the delivery and CRP levels from delivery to the first post partum day increased statistically significantly. Levels of both markers correlated significantly with duration of labor. Both amniotic white blood cells and leukocyte esterase activity increased during labor. Bacterial colonization of amniotic fluid was not clearly associated with amniotic LE‐activity or leukocyte count as determinated by Gram stain. The tests evaluated cannot be regarded as reliable methods in distinguishing intra‐amniotic infection during labor and vaginal delivery at