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Abstract Objective Interleukin‐8 concentrations in cervical secretions have been related to microbial invasion of the amniotic cavity and histological chorioamnionitis. Since a short uterine cervix may be a risk factor for intrauterine infection, we set out to determine the interrelationship between cervical‐secretion interleukin‐8 concentration, cervical length measured by transvaginal sonography and intrauterine infection in women with preterm labor and intact membranes. Design The study group comprised 144 pregnant women admitted to hospital for preterm labor and intact membranes. At admission, interleukin‐8 in cervical secretions was assayed. The uterine cervix was evaluated by transvaginal sonography and the cervical index ((funnel length +1)/cervical length) was measured. In all cases, amniotic fluid was obtained by amniocentesis immediately after cervical examination and was cultured for aerobic and anaerobic bacteria including Ureaplasma ureolyticum and Mycoplasma hominis . Placentas were analyzed at delivery for the presence of histological chorioamnionitis. Results Forty‐three per cent (62/144) of pregnancies delivered preterm and 12.5% (18/144) of the amniotic fluid cultures were positive. Placentas were available from 54 pregnancies which delivered preterm and histological chorioamnionitis was found in 59.2% (32/54) of the cases. Interleukin‐8 concentrations in cervical secretions were significantly higher in the presence of microbial invasion of the amniotic cavity (median 1191.5 ng/ml, range 812–5234 ng/ml vs. median 109 ng/ml, range 12–2231 ng/ml; p ≤ 0.0001) and histological chorioamnionitis (median 982.5 ng/ml, range 430–5234 ng/ml vs. median 435 ng/ml, range 40–1750 ng/ml; p ≤ 0.0001). Similarly, higher values for cervical index were obtained in the presence of a positive amniotic fluid culture (median 1.23, range 0.35–5.88 vs. median 0.29, range 0.024–4.85; p ≤ 0.0001) or histological chorioamnionitis (median 1.18, range 0.043–5.88 vs. median 0.562, range 0.040–2.48; p = 0.011). Multiple logistic regression analysis indicates significant independent associations with a positive amniotic fluid culture and histological chorioamnionitis for the cervical interleukin‐8 concentrations (amniotic fluid culture positive ≥850, histological chorioamnionitis ≥450) and for the cervical index (amniotic fluid culture positive ≤0.58, histological chorioamnionitis ≤0.56). Conclusions Intrauterine infection is associated with increased interleukin‐8 concentrations in cervical secretions and a short cervix. Their combined analysis may reduce the indications for invasive procedures and improve the selection of women in preterm labor who may benefit from antimicrobial treatment. Copyright © 1998 International Society of Ultrasound in Obstetrics and Gynecology