In order to study the Interleukin 1beta (IL-1beta) levels in mechanical cervical ripening with Foley catheter, IL-1beta levels in amniotic fluid of 12 women before and after cervical ripening were compared with those in 23 women in spontaneous active labour. IL-1beta was present in 81.8% of patients after cervical ripening and in none prior to it. In women with spontaneous labour 69.6% had immunodetectable IL-1beta. Women with spontaneous labour and those sampled after cervical ripening had similar IL-1beta levels in the amniotic fluid. Cervical ripening with Foley catheter is associated with high levels of IL-1beta and this probably induces labour.