The dynamic behavior of the Superphénix core was tested during commissioning of the plant. From comparison of experimental and calculated results, it was concluded that the time-dependent parameters agree quite well. The comparison is based on DYN system code calculations and on tests performed at zero power (reactivity step leading to a self-stabilization) and at power (steps on reactivity, primary flow, and secondary flow). These tests checked the behavior of the nuclear steam supply system.