Increased negative amplitudes and lack of habituation of contingent negative variation (CNV) in migraine are well established and are supposed to reflect an altered cortical excitability level. Migraine attacks occur less during pregnancy but often relapse after delivery. We investigated the effect of pregnancy on slow cortical potentials and reaction time in migraine patients and healthy controls. Four groups were examined: 14 pregnant migraine patients, 12 non-pregnant migraine patients, 15 pregnant healthy women and 16 non-pregnant healthy women aged 19-38 years. Two recordings were performed in the pregnant subjects: in the 36th week of gestation and 4 weeks after delivery. The nonpregnant subjects were recorded at the same time interval of 8 weeks. Pregnant migraine patients showed significantly fewer migraine days during the third trimester of pregnancy and returned to nearly the former level 4 weeks post delivery. Non-pregnant migraine patients demonstrated a significant reduction of migraine days at the second measurement. There was no effect of pregnancy on CNV amplitudes, but there was an effect of pregnancy on the habituation coefficient and reaction time of migraine patients. Faster habituation from a higher preactivation level was found. As an explanation for the changed habituation level we favour the model of correlation between preactivation level and habituation level, the so-called law of initial value. We found a correlation between preactivation level and habituation. Our study confirms a specific effect of pregnancy on slow cortical potentials in migraine patients.