To suppress uterine contractions during cervical ripening induced by prostaglandin E2 (PGE2) gel, .beta.-mimetic drugs [fenoterol, ritodrine and clenbuterol] were given orally 30 min before PGE2 application to 17 patients with unripe cervix. This prevented the increase in contraction frequency observed during the first 4 h after PGE2 application in 17 controls. Nevertheless, cervical ripening proceeded at a similar rate and the clinical outcome was comparable in both groups. Prostaglandin E2 application caused a transient rise in plasma levels of the PGE2.alpha. metabolite (13,14-dihydro-15-keto), which was not prevented by pretreatment with .beta.-mimetics. Patients with premature rupture of the membranes had higher initial plasma PGF2.alpha. metabolite levels than those with intact membranes but cervical ripening proceeded with the same rate; the effect of .beta.-mimetics was the same in both groups. Cervical ripening induced by PGE2 does not depend on uterine contractions; increased production of PGF2.alpha. is unrelated to the ripening process. There was no difference between the 3 .beta.-mimetic agents in the present study.