Periodic patterns of mixed-mode oscillations with successive numbers of small-amplitude oscillations followedby one large-amplitude oscillation (period-adding phenomenon) have been observed in the asymptotic regimeof the Belousov−Zhabotinsky reaction (bromate−malonic acid−ferroin) in a CSTR (continuously stirredtank reactor) at decreasing residence times. Such period adding has been predicted by a simple model proposedrecently for a qualitative description of asymptotic and transient oscillations observed in the BZ system.Patterns qualitatively corresponding to the experimental ones are obtained in this model.