A gas chromatographic/mass spectrometric method for measuring chlorpromazine using 2H6--labeled chlorpromazine as an internal standard has the potential for considerable precision and specificity. Results are reported of chlorpromazine levels in plasma and saliva after administration of a single test dose to 13 schizophrenic patients in a tightly designed experiment. There was a clear and substantive relationship between blood and saliva levels of chlorpromazine, both following a typical decay curve. Saliva and plasma levels were strongly associated for a particular patient, and there was even a strong consistency in saliva-plasma ratios between patients, with an overall statistically significant correlation between plasma and saliva levels for all measurement on all 13 patients. In general, it seems that saliva sampling has great potential as a simple noninvasive technique for investigation of chlorpromazine and other antipsychotic drugs in psychotic patients. Nevertheless, for the moment, it should be regarded as strictly experimental and not suitable for immediate clinical application.