A woman taking haloperidol develops a spectrum of adverse effects that include the amenorrheagalactorrhea syndrome and extrapyramidal dysfunction, including bradykinesia, muscle rigidity, and tremor at rest. Her psychiatrist prescribes a newer antipsychotic drug that improves both positive and negative symptoms of schizopherenia with few of the side effects that result from dopamine receptor blockade. Since weekly blood tests are not deemed necessary the drug prescribed by the psychiatrist is probably