Diphenylhydantoin (PHT) and primidone (PRM) were determined by the EMIT technique in the plasma, tears, saliva, and CSF of epileptic patients. Results indicate for PHT that tear values are more strictly correlated than are the saliva values to plasma and CSF concentrations. As for PRM, the data obtained show great interindividual variability of concentration in the different body fluids--in agreement with the wide range of both protein binding and half-life of this drug.