The relationship between chronic oral dosage with a long-acting formulation of propranolol and plasma propranolol levels 22 to 23 hours later is described in 12 adult male patients with organic brain disease. Separately, the effects on plasma levels of thioridazine plus metabolites with concomitant rising dose long-acting propranolol administration were studied in five patients. Significant dose-related increases in levels of thioridazine and metabolites were found when long-acting propranolol was given. No changes in haloperidol levels were found in three patients studied in a similar protocol.