The paper concerns the situation in which, for a considerable time, the onset of each respiratory cycle coincides with one and the same section of a cardiac cycle. A standardized procedure is described with which, in anesthetized rabbits, the potentiality of the biological mechanisms responsible for the phenomenon may be quantified. The procedure consists of progressively prolonging the cardiac cycles by selectively cooling the sinus node. Care is taken that during such procedure a situation is passed in which the respiratory cycles are a multiple of the cardiac cycles. The synchronizing kybernetic system, if any, must click in, then. As the prolonging of the cardiac cycles continues, the synchrony will get lost the sooner the weaker the potentialities of the kybernetic system and vice versa. Four drugs are tested as to their potential action on the kybernetic system. Nikethamide and methylphenidate tend to decrease its efficacy, allobarbital and benzoctamine tend to increase it, none of them, however, being conclusively effective.