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Interoceptive sensations, that means, perceptions of the physiological body state, play an important role in the generation and expression of emotion. The focus of the research presented here is on respiratory sensations as specific interoceptive signals. Such respiratory sensations (like the feeling of dyspnea) play an important role in symptom perception in somatic (e.g., asthma) as well as in mental disorders (e.g., anxiety disorders). There are several different ways to manipulate respiratory sensations in an experimental environment, but many of them did not equal sensations in daily life. Here, stimuli (inspiratory resistive loads, caffeine) were used that trigger nearly naturally occurring interoceptive sensations. Taking into account that the elicited interoceptive experience also induces an unpleasant feeling state it is most likely that individuals show defensive physiological responding to such cues and try to avoid them. According to a bidirectional motivational system defensive behaviors are regulated by a defensive motivational system that is activated by threatening cues. From research with exteroceptive stimuli it is known that defensive responding is typically characterized by heightened autonomic arousal, increased respiration, and a potentiated startle eyeblink response. In contrast, only a few studies using interoceptive stimuli have incorporated the measurement of physiological data in their experimental designs. If included, studies show also heightened autonomic responding, whilst a heterogeneous respiratory as well as startle eyeblink responding is observed. Thus, the studies presented here were designed to clarify the factors that mediate defensive responding to interoceptive sensations. Study 1 investigated the influence of anxiety on the subjective, respiratory, and autonomic response to an individually determined inspiratory resistive load, while study 2 focuses on the effect of attentional modulation of the startle eyeblink response to a mild respiratory threat. In study 3 the modulation of subjective, respiratory and autonomic reactions by arousal expectations was examined. Therefore, caffeine, a respiratory stimulant, or a placebo were administered without the participants’ knowledge. The fourth study examined the influence of the process of worrying, a strategy to deal with unpleasant body symptoms, on defensive responding. Depending on the study design subjective, respiratory and autonomic (skin conductance level, heart rate) parameters were assessed as marker for defensive mobilization. In study 2 and 4 the startle eyeblink response was measured as further index of defensive activation. Besides that in study 2 also the P3 component of the event-related potential, as an index for attentional allocation, was recorded. The main findings of the presented dissertation are the following: Study 1 revealed that 1) only high anxiety sensitive individuals reporting also high suffocation fear respond to lower stimulus intensities with stronger defensive responding, and 2) that this group demonstrated a maladaptive compensatory breathing pattern. Additionally, study 2 exhibited that 1) the startle eyeblink response is relatively inhibited during a mild interoceptive threat, and 2) this inhibition corresponds to an attention allocation towards breathing as indicated by a reduced P3 amplitude to the startle noise as well as subjective report. Furthermore, highly anxiety sensitive individuals showed a more pronounced defensive responding if the interoceptive sensations were unexpected (study 3). Recently, study 4 demonstrated that worry led to an increased defensive response mobilization. All studies are discussed in the context of the theoretical background of the defensive response modulation to exteroceptive and interoceptive sensations with respect to mediating factors. Showing exaggerated defensive responding and maladaptive adaptation processes in high anxious individuals the results point towards the important role of interoceptive sensations in the etiology, maintenance and therapy of mental disorders, especially the anxiety disorders.