OBJECTIVE To evaluate the safety of edrophonium chloride in the course of the Tensilon test by measurement of hemodynamic and ECG parameters and the observation of adverse events. METHODS 25 patients with known or suspected myasthenia gravis were included in an open, prospective study concerning the performance of the Tensilon test. Blood pressure, heart rate, continuous ECG and adverse events were recorded 10 minutes following intravenous application of Tensilon. RESULTS Blood pressure and heart rate did not change significantly during the observation period. One patient on beta-blockers developed a grade I AV block. Self-limiting adverse events of short duration were observed in 11 patients. Serious adverse events such as syncope or hemodynamic deterioration did not occur. CONCLUSIONS The Tensilon test appears to be a safe procedure. A detailed clinical cardiac history, the history of medication and twelve lead ECG recordings should be documented in all patients undergoing the Tensilon test. Patients with a history of dysrhythmia receiving digitalis, beta-blocking agents or Ca antagonist therapy should be managed with special care, as Tensilon enhances vagal effects.