Propranolol glycol is a major metabolite of propranolol in man with potent anticonvulsant activity. Propranolol glycol appears to be more potent for this effect than propranolol. The onset of action of propranolol glycol is instantaneous but delayed for propranolol. Maximal anticonvulsant activity for propranolol glycol is obtained immediately and for propranolol 10 minutes after administration. The delayed onset of this action of propranolol and the immediate anticonvulsant activity of propranolol glycol strongly suggest that the anticonvulsant properties of propranolol may be related to its conversion to propranolol glycol. Propranolol and propramioiol glycol have a similar spectrum of gross behavioral effects ranging from quietness at low doses to paralysis at high doses. These observations suggest the possibility that propranolol glycol may be contributing to some of the therapeutically significant effects of propranolol in the central nervous system.