Clozapine, a powerful neuroleptic with unique clinical efficacy (and without parkinsonic side effects), has been shown to have an unusual EEG profile. The EEG changes after clozapine, especially when instrumentally quantified, demonstrated the predictive value of EEG. The similarities of the EEG profile of clozapine with the profile of thymoleptic compounds indicated its possible thymoleptic effect. This later proved to be the case with therapeutic studies in depression. The EEG profile of clozapine in volunteers is similar to the EEG profile in schizophrenics (with appropriately higher doses). Instrumental quantification was performed with spectral and iterative interval analysis to show the advantages of each method and also the complementary value of both of them.