Baseline quantitative electroencephalographic (QEEG) characteristics and their changes after a single test dose of either haloperidol or clopenthixol were investigated in a group of 29 schizophrenics as possible predictors of short-term response to those drugs. On baseline QEEG assessment, responders (R) to subsequent treatment showed fewer slow and more fast activities than nonresponders (NR). A large overlap between R and NR with respect to these measures was observed, however, revealing their practical inadequacy to predict short-term response in individual patients. On the contrary, changes in alpha 1, observed 6 hr after the administration of a single test dose of either haloperidol or clopenthixol, discriminated to a very large extent between R and NR, correctly identifying 17 out of 18 R and 8 out of 10 NR. The QEEG test dose procedure might be used in the selection of the most appropriate antipsychotic drug for individual schizophrenic patients.