Despite the widespread use of carbamazepine (CBZ) in the treatment of a number of neuropsychiatric disorders, its mechanism(s) of action remain to be elucidated. In view of the postulated interaction of CBZ with peripheral type benzodiazepine (BDZ) receptors and the role of these receptors in regulating neuroactive steroid biosynthesis, we investigated the effects of CBZ on pregnenolone accumulation in cultured rat C6 glioma cells. We found that CBZ elevates pregnenolone accumulation over a period of 60 min, and that this effect was not due to inhibition of pregnenolone metabolism. Preincubation of C6 cells with the selective peripheral type benzodiazepine receptor antagonist PK11195 blocked the CBZ-induced elevation in pregnenolone-induced elevation in pregnenolone accumulation. The results suggest that CBZ stimulated pregnenolone biosynthesis in cultured C6 cells involves a direct or indirect interaction with peripheral type benzodiazepine receptors. These effects may provide additional insights into the mechanisms by which CBZ regulates neuronal excitability. Depression 3:267-y (1995/1996). © 1996 Wiley-Liss, Inc .