A model is developed to investigate the response of a coupled two-core reactor to a neutron pulse. Various coupled cores with symmetrical and asymmetrical configurations and compositions are studied. The fundamental spatial mode splits into two distinct decaying submodes. The reactivity of a coupled-core system is defined, and two methods are given for its measurement. The model is compared with results of pulsed-neutron experiments performed on a light-water-moderated, coupled, compact two-core reactor fueled with uranium of 90% 235U content and reflected by both light water and graphite in either symmetrical or asymmetrical configurations