2 groups of chinchillas ( Chinchilla lanigera) were trained to avoid shock (1.6 mA or 3.0 mA) in a two-way shuttlebox. The less intense US produced substantially superior avoidance acquisition. The higher US intensity generated an unexpected increase in the level of intertrial responding during extinction training. This effect was interpreted in terms of the extinction of “freezing” responses which appeared to account for the inferior avoidance acquisition of the higher US group. Unlike other representatives of the order rodentia which have been subjected to shuttlebox avoidance training, the chinchilla displays a performance which is at least comparable to the optimum performance of the rat.