One hundred and six third trimester pregnant women with prelabour rupture of membranes preterm were randomised to either peroral amoxicillin 0.75 g 3 times daily (n = 50) or placebo (n = 56) in a blinded way. The patients were hospitalised in bed for 7 days unless contractions started and delivery ensued. Only 1 patient was discharged after 7 days of treatment, while the remaining ones delivered within 1 week after admission. The average rupture-to-expulsion interval was 68.4 h in the placebo group and 91.7 h in the amoxicillin group, implying a significantly prolonged stay by 43% in the amoxicillin group (p = 0.03). The other outcome variables registered (birth weight, stillbirth prevalence, vaginal haemorrhage and postpartum endometritis-myometritis) did not differ significantly in the two treatment groups. There was a trend towards a longer duration of stay in the neonatal ward among newborns in the amoxicillin group suffering neonatal death (p = 0.06). It is concluded that antibiotic treatment of this group of women may be justified in settings were sexually transmitted diseases and other genital infections are prevalent, whereas such treatment is less likely to have an effect when genital infection is rare.