The excretion of carbamazepine in the saliva of six normal adults after receiving a single oral dose of 400 mg carbamazepine is described. There was a good correlation between carbamazepine concentrations in the plasma and saliva (r = 0.94, P less than 0.001). This indicates that the concentrations of carbamazepine in the saliva can be used to monitor carbamazepine therapy. The half-life of carbamazepine in the plasma was not significantly different from the half-life in the saliva. Thus areas under concentration-time curves, apparent volumes of distribution (Vd) and the total body clearances were significantly dependent (P less than 0.001) upon the distribution of carbamazepine between plasma and saliva. Calculated from saliva concentrations, 75% of the total carbamazepine plasma concentration is bound to protein while 25% is unbound in diffusional equilibrium with saliva. These figures are consistent with data in the literature.