Although previous evidence suggests advantages of nifedipine over terbutaline as tocolytic agents, in some jurisdictions, terbutaline is approved for use and nifedipine is not. In women in preterm labour, we compared the impact of terbutaline versus nifedipine on inhibition of uterine contractions, preterm birth, neonatal sepsis, intracranial haemorrhage or necrotizing enterocolitis, death or admission to a neonatal intensive care unit and maternal adverse reactions. We randomized 32 women to nifedipine and 34 to terbutaline. We found no difference between groups in tocolysis or preterm birth. No serious maternal adverse effects or serious neonatal adverse outcome occurred in either group. Less serious maternal adverse effects less common with terbutaline included flushing (2.94% versus 43.7%) and headache (5.9% versus 31.2%). The administration of terbutaline increased tremor (76.4% versus 0%), nausea (58.8% versus 9.4%) and dizziness (29.4% versus 6.25%). The total number of side effects, and the proportion of women experiencing one or more side effects, proved greater with terbutaline. In this study, terbutaline and nifedipine performed similarly in their tocolytic effects. Each drug has specific side effects, although overall, nifedipine was associated with fewer adverse effects.Premature birth is common (over 5% and, in some countries, over 10%) [1,2] and is responsible for approximately 75% of all neonatal deaths and 50% of childhood neurological morbidities [3,4]. Preterm infants often require intensive care that is associated with emotional and economic costs to both the family and society [5].Approximately 75% of preterm birth is attributable to spontaneous preterm labour [1]. Delay in preterm labour therefore provides a potential opportunity for decreasing neonatal morbidity and mortality [6].The optimal medical management of threatened preterm labour is controversial [7]. Despite theoretical benefits of keeping the foetus in utero long enough to enable administration of a full course of corticosteroids to assist in foetal lung maturation, and to organize transfer to an appropriate neonatal care unit, no agent has been shown to improve neonatal outcome [2,7]. Thus, the choice of therapy has focused on delay in delivery and minimization of adverse effects.The drugs registered for tocolysis include the b adrenoceptor agonist ritodrine (United States and Europe), terbutaline (Brazil) and the oxytocin receptor antagonist atosiban (Europe) [8]. Calcium channel blockers (nifedipine) and cyclooxygenase inhibitors (indomethacin) are also used for inhibiting preterm labour although, in many countries, they are not currently registered for this indication [9].Betamimetics (isoxsuprine, ritodrine, terbutaline, fenoterol and salbutamol) delay labour [10][11][12], but their use has been limited by a high incidence of maternal adverse effects [10,13,14]. Many centres use nifedipine, which also has established effectiveness in delaying labour [15] and has advantages of oral administration and relatively low...