Six menstrual cycles and three 1-month periods were studied in seven patients with epilepsy. The patients all had had anti-epileptic treatment for a long time. In each case, the dosages had been costant for at least 1 month prior to the start of the investigation.

Blood samples were taken every second day. Phenytoin, phenobarbital, carbamazepine, estradiol and pregesterone were analyzed. The serum levels of the anti-epileptic drugs were correlated to the plasma hormone concentrations.

No correlations were obtained between the plasma hormone concentrations and the serum levels of the anti-epileptic drugs. There is, therefore, no evidence that the relationship between the seizure frequency and plasma hormone concentrations, shown in a previous study (Bäckström 1976)) was related to a change in serum levels of the anti-epileptic drugs.