The exposure to a static magnetic field of 80+/-20 Gauss (8+/-2 mT) resulted in the inhibition of Serratia marcescens growth. Callus cell suspensions from Hordeum vulgare and Rubus fruticosus were also examined and only the former was found to be affected by the magnetic field, which induced a decreased viability. S. marcescens was shown to be virulent only toward H. vulgare and this virulence was reduced by the presence of the magnetic field. The modification of glutathione peroxidase activity under the different experimental conditions allowed us to speculate on the possibility of an oxidative-stress response of H. vulgare both to S. marcescens infection and magnetic field exposure. Since the control of microbial growth by physical agents is of interest for agriculture, medicine and food sciences, the investigation presented herein could serve as a starting point for future studies on the efficacy of static magnetic field as low-cost/easy-handling preservative agent.