AbstractPrevious studies found that elimination of the geomagnetic field (GMF) interferes with the normal brain functions, but the underlying mechanism remains unknown. The present study examined the effects of long‐term exposures to a near‐zero magnetic environment on the noradrenergic activities in the brainstem of golden hamsters. Both the content of norepinephrine (NE) and the density of NE‐immunopositive neurons in the tissue decreased significantly after the treatment, and the effects could be progressive with time. These variations may substantially contribute to behavioral and mood disorders reported in other studies when animals are shielded from the GMF. Bioelectromagnetics © 2006 Wiley‐Liss, Inc.