The present paper reports on five patients who developed apathy as a peculiar side effect of antidepressants. Their behavioral and psychopathological changes were primarily due to the near-absence of emotional experience, a key characteristic that distinguishes apathy from avolition and abulia. The emergence of apathy in the course of an antidepressant treatment should raise the suspicion of an adverse effect of the drug and lead to its prompt withdrawal. A sample of the relevant clinical evidence favoring the distinction of apathy confined to a single sensory domain ("unimodal apathy") from apathy confined to more than one sensory realm ("multimodal apathy") is reviewed. From a pathophysiological standpoint, it would appear that neural nets centered in the amygdala-temporo polar cortex are critical for the integration of sensory perceptions and mental imagery with appropriate emotional tone and quality as well as with their accompanying somatic markers, as they receive afferents from the major projection systems of the prosencephalon and lie in nodes strategic to modify the ongoing activity of multiple parallel brain systems. The fact that one common symptom can be produced by such a heterogeneous family of substances points to a shared neurochemical mechanism of action. At present, discrete cerebral serotoninergic circuits would appear to be suitable candidates for such a role. Cases as these may be critical for the understanding of the cerebral organization of emotions in man, lending support to the notion that distinct neurochemical systems mediate discrete psychopathological symptoms.