Platelet-activating factor (PAF) is involved in such reproductive processes as parturition. We investigated the effect of PAF on the expression of matrix metalloproteinase-1 (MMP-1) and that of tissue inhibitor of metalloproteinases-1 (TIMP-1) in human uterine cervical fibroblasts. Uterine cervical tissue was obtained from patients who underwent cesarean section at term. Collagenase-dispersed fibroblasts were cultured and used in the experiments. PAF receptor was identified in the uterine cervical fibroblasts by use of reverse transcription-polymerase chain reaction and Southern blot analysis. Northern blot analysis showed that PAF increased the expression of MMP-1 mRNA in a time-dependent manner, whereas expression of TIMP-1 mRNA was not affected by PAF. Concentration of MMP-1 protein in the PAF-treated culture media significantly exceeded that in control cultures. The PAF-induced production of MMP-1 protein was abolished by treatment with WEB 2170, a specific PAF receptor antagonist. Results suggest that PAF may accelerate collagenolysis in the human uterine cervix by inducing an imbalance in the activity between MMP-1 and TIMP-1, thus contributing to the cervical ripening during parturition.