Brief exposure to moderate intensity static magnetic fields has been shown to produce a transient alteration in physiological function in a variety of biological systems, primarily those related to changes in intracellular Ca²⁺. In the present study GH3 cells were cultured during continuous exposure to a 0.5 T field, for periods of up to 5 weeks. Following a 1‐week exposure, cell growth declined by 22% and returned to control levels in 1 week. This was not statistically significant but, with a 4‐week exposure, a statistically significant decline in growth of 51% was observed and return to control levels did not occur for 4 weeks. Cell diameter, on the other hand, significantly increased following 3 weeks of exposure and did not return to control levels for 3 weeks after termination of exposure. Ca²⁺‐dependent changes in the dynamic reorganization of the actin cytoskeleton are suggested as the probable explanation for these observations. Bioelectromagnetics 30:114–119, 2009. © 2008 Wiley‐Liss, Inc.