Tocolytic agents have limited efficacy, delaying preterm delivery by 48 hours to 7 days, without any neonatal benefit. Cyclo-oxygenase inhibitors and calcium canal inhibitors seem to be the most efficient. Betamimetics are tocolytic agents with the highest incidence of severe maternal side effects. Oxytocin receptors antagonists and cyclo-oxygenase inhibitors are tocolytic agents with the best maternal tolerating profile. Nifedipin is the tocolytic agent presenting the best fetal tolerating profile. However, doubts persist on fetal and neonatal tolerance for cyclo-oxygenase inhibitors and probably even for oxytocin receptors antagonists. A combined or sequential tocolytic treatment did not prove superior to a single tocolytic treatment although the former is also associated with a high incidence of severe adverse maternal effects. Nevertheless, this low efficiency should not make us forget their major interest in case of premature labour: to allow the mother's in utero transfer to a level II or III maternity following the gestational age, and moreover to gain time so as to obtain an optimal interval for the fetal lung maturation by corticoid injection. Tocolytic agents should be used between 24(+0) and 34(+6)weeks of amenorrhea. They should be used on the short term (24 to 72 hours) owing to their short period of efficacy and to the risk of side effects that increases with the duration of use.