Nine healthy subjects received 400 mg sodium valproate orally in the fasting state. Binding parameters of valproic acid to serum proteins were determined by Scatchard analysis for individual series of valproic acid data. Total and unbound (intrinsic) clearances (CLt and CLu) were calculated by dividing the dose by the appropriate area under the serum drug concentration-time curve. Unbound clearance correlated positively with the product of association constant (Ka) and concentration of free protein ((P)) (P < .05). Conversely, no significant correlation was found between CLt and binding parameters. The average unbound concentration correlated negatively with both CLu and ka(P) values. The result indicates an effect of CLu on Ka(P) value of valproic acid.