Interest in magnetic fields has been stimulated in recent years by concern over the physiological effects they may have on humans and animals and the deleterious effects they have on the performance of some electrical equipment, particularly video display units. Investigations have yielded results which are presented in this report as reference values. Note 1 – The European Union EMC Directive has prompted magnetic field measurements, particularly in respect of the commercial office environments associated with supply authority substations and electrical distribution systems within buildings. Supply authorities have sponsored most of the work and the results are generally within the frequency range of 50 Hz to 2 kHz, and presented as r.m.s. values. There is, however, a need to have some knowledge about d.c. fields and the fields up to 150 kHz as they may interfere with some types of equipment. Note 2 – Most of the magnetic field data in this report is associated with sinusoidal current sources and r.m.s. values may be assumed unless otherwise stated. Power supply systems operating at voltages less than or equal to 1 000 V are designated low-voltage, those above 1 000 V and up to 35 kV are designated medium-voltage, and those in excess of 35 kV are designated high-voltage.