[An experimental pain model: the formaldehyde test].

Some papers have been published in relation to alternative models of experimental pain in animals. In this work, with the aim of proving the validity, safety, reproducibility and objectivity of this model, we have compared the behaviour of the animal under the formaldehyde test before and after the intracerebroventricular administration of morphine, proving itself as an ideal model for the study of chronic pain caused by an excess of nociception.