Central, peripheral and cardiac side-effects of both anticholinergic drugs atropine and glycopyrrolate were compared during the antagonism of muscle relaxation with pyridostigmine. In a randomized, double-blind fashion 50 patients were given 10 micrograms/kg of atropine and 50 were given 5 micrograms/kg of glycopyrrolate with 125 micrograms/kg pyridostigmine intravenously. Continuous Holter ECG-monitoring over 3 hours was performed. The procedure was divided into the following phases: control (5 minutes before application of antagonists), phase I (application of antagonists and the following 5 minutes), phase II (subsequent 30 minutes), phase III (until 3 hours had passed). The first 32 minutes were subdivided into periods of 4 minutes. Analysed were: 1st: The number of patients with supraventricular, junctional and ventricular beats, 2nd: The mean heart rate per period, 3rd: The incidence of central-anticholinergic syndromes and the peripheral antimuscarinic side-effects. Supraventricular beats were found after atropine in 42 patients and after glycopyrrolate in 18 patients (p < 0.001). The differences mainly occurred during phase I (atropine 15 vs. glycopyrrolate 4 p < 0.05) and III (atropine 38 vs. glycopyrrolate 18, p < 0.01). Junctional beats were found after both drugs (atropine 7 vs. glycopyrrolate 10), above all during phase III. Ventricular beats were observed after atropine (21) and glycopyrrolate (18). Atropine as well as glycopyrrolate caused an increased heart rate within the first 4 minutes (atropine 47% vs. glycopyrrolate 27%, p < 0.01). During phase III after atropine, the heart rate decreased below the control value (p < 0.05). None of the patients showed central anticholinergic syndromes after either drug.(ABSTRACT TRUNCATED AT 250 WORDS)