The purpose of this experiment was to compare components of the human and rat auditory event-related potential (erp) in a serial feature-positive discrimination task. Subjects learned to respond to an auditory target stimulus when it followed a visual feature (x ? a+), but to not respond when it was presented alone (a-). Upon solving the task, the n2 component, which has been suggested to reflect the activation of inhibitory processes, was temporarily more negative in response to the target on a- than on x ? a+ trials in both species. However, whereas a p3 component was present in the human participants, this component was absent in the rats. In both species, the amplitude of several erp components, including the n2, decreased in the course of training. These results are discussed in the framework of contemporary models of associative learning.