A single-fibre electromyography measuring unit based upon a personal computer (Apple II) and a special triggering unit is described. Its compact size facilitates its use online, next to the patient. It is a relatively cheap system, and can be handled by one investigator and a nurse. Operation is simple, and error messages are provided. Investigation of a patient consists of measuring the time of occurrence of action potentials in up to 20 trains of complex motor unit action potentials (MUAPs). One train may consist of up to 170 MUAPs, each comprising a maximum of four single action potentials (spikes). Triggering is performed with a special unit: after an initial spike, triggering at an adjustable level is only possible within an adjustable time window. This feature reduces false triggerings and allows selection of a part of a complex MUAP. Interval analysis by the computer also reduces processing of MUAPs originating from other motor units. Computed are the mean consecutive difference (MCD) values of the jitter, the variance, the percentage of blockings and the number of relevant intervals. Scatter plots can be displayed and printed of the raw data, the consecutive differences or the interpulse intervals (IPI) against the interdischarge intervals (IDI). Suspicious data may be rejected by manipulation of graphical cursors. If a MUAP consists of at least four spikes, a test can be carried out whether there is a neurogenic variability cause: concomitant jitter. The system has been evaluated over the last two years in the EMG department of the Academic Hospital, Utrecht, The Netherlands. A single-fiber electromyography measuring unit based upon a personal computer (Apple II) and a special triggering unit is described. Its compact size facilitates its use online, next to the patient. It is a relatively cheap system, and can be handled by one investigator and a nurse. Operation is simple, and error messages are provided. Investigation of a patient consists of measuring the time of occurrence of action potentials in up to 20 trains of complex motor unit action potentials (MUAPs). O