Transient hyperprolactinaemia has been reported to follow unprovoked seizures, a finding proposed to be useful in the differential diagnosis of epilepsy. There is also evidence that patients with unprovoked seizures may have high baseline prolactin levels, which could be of value in detecting those predisposed to epilepsy after a first convulsive attack. The purpose of this study was to examine whether prolactin levels are elevated: (1) postictally in febrile seizures and (2) interictally in afebrile seizures. In 17 children with simple febrile seizures, mean postictal prolactin value (370 +/- 160 mU/l, mean +/- SD) was significantly higher (approximately 0.001) than the mean baseline value of 18 seizure-free controls (202 +/- 136 mU/l). The mean baseline prolactin values were not significantly different: (1) in ten children with afebrile versus ten seizure-free controls and (2) in 18 children with febrile seizures associated with high risk for subsequent afebrile seizures versus 23 children with febrile seizures but unlikely to suffer from afebrile seizures. CONCLUSION. Postictal prolactin levels may be a useful marker of recent febrile seizures, while baseline prolactin levels do not appear to have any prognostic significance in afebrile seizures.