Magnetic fields were found to have a profound effect on the dynamics of the oscillating peroxidase-oxidase (PO) reaction. Static magnetic fields up to 3000 G were applied to this biochemical reaction, and their effects on the oscillatory dynamics were investigated. When the system is in a simple periodic state, magnetic fields induce a decrease in the oscillation amplitude. When the system is in a state of complex dynamics magnetic fields may induce a shift in dynamics to a neighboring state. Thus, magnetic fields may be used for noninvasive manipulations and control of complex dynamics.