Twenty-three serum samples and 13 saliva samples from 14 Chinese epileptic patients treated with phenytoin (DPH) were obtained to study the correlations between total, free serum, and saliva DPH concentrations. The binding of DPH to serum protein was assessed by equilibrium dialysis, and total and free DPH concentrations were analyzed with a domestic fluorescence polarization immunoassay reagent by the TDx system. A strong correlation existed between the total and free concentrations (r= 0.90, n = 20,p< 0.001). The mean value for the DPH free fraction was 11.13 ± 3.65%. The mean, value for the saliva fraction was 9.40 ± 2.60%. This is the first attempt to monitor free DPH concentrations in serum in Chinese patients.