Summary: Preliminary studies with the radioreceptor assay for neuroleptics suggest several advantages of this technique. Consistent with results obtained with other techniques, it is obvious that there is variation among individuals in terms of the serum levels obtained on given oral doses of neuroleptics; in addition, total daily dose correlates poorly with serum levels. The radioreceptor assay technique, however, is relatively uncomplicated and inexpensive and relies on methods that are commonly used in general hospital laboratories. Unlike gas chromatography/mass spectrometry, gas-liquid chromatography, and even radioimmunoassay—which are highly discriminative—the radioreceptor assay detects both parent drugs and active metabolites of virtu-ally all classes of neuroleptics on the basis of their presumed physiologic mechanism of action.