The effect of a 50 Hz magnetic field on the growth of different bacterial strains was studied. We used bacteria with different cell shapes. We compared rod-shaped bacteria (E. coli, L. adecarboxylata) and spherical bacteria (S. aureus, P. denitrificans, S. paucimobilis, R. erythropolis). The growth curves of control and magnetic fields exposed samples were measured. The cylindrical coil induced magnetic fields with inductions up to 10 mT. Duration of exposure varied up to 24 min. Exposure took place at laboratory temperature (24–26°C) and the air ventilator maintained the temperature of sample. We observed the decrease of optical densities in exposed samples. The magnetic field effect was bigger for rod-like bacteria. We concluded that magnetic field effects depend on the shape of exposed cells.