Little has been written on the analysand's failure to act in the session when some form of motoric reaction or behavior seems appropriate and expectable. This phenomenon is conceptualized as negative acting in. Several clinical vignettes are provided. The importance of analytic interventions at these moments of behavioral omission, the possible countertransferential interferences, and the frequent use by the patient of rationalizations are commented on. The point is made that even though the exploration of these nodal points does not always lead to the discernment of psychodynamics, it usually contributes to the fostering of ego-observing capacities. Detection of episodes of negative acting in may pose special difficulties for the analyst, since it requires that attention be focused on events that do not take place, but their exploration is considered important for an analysis of the patient's psychic life.