Oxcarbazepine, a new drug with antineuralgic properties has been evaluated in a long-term follow-up of 6 patients (2 males, 4 females; aged 42-77 years; mean 61 years), previously reported on with trigeminal neuralgia. Daily oral oxcarbazepine dose correlated significantly with both total oxcarbazepine (r = 0.851) and 10-OH-carbazepine (r = 0.958) serum concentrations. Mean percent free oxcarbazepine and 10-OH-carbazepine was 41 and 61% respectively and there was no significant difference in binding between male and female patients. Free serum concentrations of oxcarbazepine and 10-OH-carbazepine correlated significantly with total serum oxcarbazepine and 10-OH-carbazepine respectively, indicating that binding capacity of both are essentially constant within the respective ranges of 0.2-11.4 mumol.l-1 and 20-150 mumol.l-1 observed in the present study.