Although heartburn, thought to indicate reflux of gastric contents into the oesophagus, occurs frequently in pregnant women during the last trimester, its aetiology is not clear. Prolactin blood concentrations rise progressively during pregnancy and heartburn is known to disappear spontaneously during the last weeks of pregnancy. In view of this and other factors, motility studies and estimation of serum prolactin levels were carried out on 20 pregnant Black women. Results show that patients with prolactin levels over 3,000 microunits/ml had significantly higher mean barrier presures (sphincter pressure-gastric pressure) than the patients with hormone levels of less than 3,000 microunits/ml (P less than 0,02). No direct correlation could, however, be demonstrated between barrier pressures and prolactin levels (r = 0,3494). It is concluded that further studies would seem to be indicated on an animal model to establish the importance of prolactin in the regulation of the lower oesophageal sphincter tone.