This article analyzes the effects of lesions to the medial parabrachial nucleus (PBNm) in taste aversion learning (TAL) and taste discrimination tasks (TDT). In the first experiment, control and lesioned rats were presented with a delayed TAL task in which presentation of the gustatory stimulus was followed 15 min later by the intragastric administration of LiCl. In the second experiment, ingestion of the gustatory stimulus was followed immediately by LiCl administration. Control animals successfully learned both tasks, whereas PBNm-lesioned animals learned only the second task. In the third experiment, the animals were subjected to TDT with water, saccharine, and quinine. The lesioned animals ingested significantly different amounts of stimuli from that ingested by control rats, showing a clear preference for high concentrations of saccharine; the lesioned animals rejected high concentrations of quinine to a lesser degree than did control animals. In a fourth experiment, PBNm-lesioned animals were able to solve a delayed TAL task when discriminated gustatory stimuli were used. These results are interpreted as evidence that the PBNm lesion interferes with gustatory processing and that the temporal demands imposed by Experiment 1 obviate the use of exteroceptive cues.