2 Daily fluctuations in serum levels of carbamazepine and carbamazepine-10,11-epoxide did not appear to be related to the dosage schedule, but some patients tended to have lower fluctuations when the carbamazepine was given more frequently.

3 The epoxide/carbamazepine serum ratios varied greatly from patient to patient, and also fluctuated during the day for the same patient.

4 Carbamazepine and carbamazepine-10,11-epoxide were present in CSF in concentrations ranging from 19 to 34% and 26 to 71% of the serum concentrations, respectively.

5 There was a significant relationship between the free fraction of both drugs evaluated in vivo and the CSF/serum ratios.

6 The need for a careful evaluation of the possible clinical effect of the epoxide is stressed.