The aetiology of brain tumours is not well understood. Ionizingradiation and a genetic predisposition have been implicated asrisk factors, however, they are thought to account for a smallproportion of all such tumours.1Positive associations betweenbrain cancer and other occupational exposures such as vinylchlorides,2–4pesticides5and electromagnetic fields6have beenobserved in some studies, but, taken as a whole, the results areinconclusive. Efforts to clarify the role of these factors are needed,particularly in light of the extremely poor prognosis for patientsdiagnosed with these neoplasms.7During the past decade, a number of studies have examinedthe relationship between occupational exposure to magneticfields and the occurrence of brain tumours. Several of thesestudies were performed within electric utility industry workersand incorporated detailed exposure assessments obtained usingeither personal monitoring devices or other sampled measures