AbstractThe interaction of atropine or methylatropine with a barbiturate was studied in male rats. Different doses of the cholinergic blocking agents were given prior to an anaesthesia threshold determination with hexobarbital. The dose of hexobarbital needed to induce a burst suppression in the EEG which was 1 second or longer (the “silent second”) was used as the threshold. The ensuing anaesthesia times were also measured. Methylatropine in doses up to 8 mg/kg had no discernable effect on the threshold within 5 hrs after the dose. Atropine decreased the threshold 1.5 hr after the administration. The maximal effect was obtained with the largest dose given (8 mg/kg, fig. 2). Both cholinergic blocking agents decreased the body temperature. No measurable effects were obtained on the ensuing anaesthesia times. The synergistic effect found between atropine and hexobarbital in the present experiments is probably brought about through actions in the central nervous sys