In opiate-dependent rats previous studies showed that anaesthetic agents, such as chloral hydrate, midazolam and ketamine interfere with naloxone-precipitated opiate withdrawal. Each anaesthetic induces a specific pattern of interference, indicating that the interference is agent-dependent. In order to further investigate these effects and highlight a potential pharmacological basis of opiate withdrawal interference through anaesthetic agents, we hypothesized that anaesthetic-mediated interference of opiate withdrawal is also dose-dependent. Three groups of rats were compared in an experimental procedure of rapid withdrawal induction by an antagonist under anaesthesia using sub-anaesthetic dosage of midazolam, ketamine or saline. We observed that sub-anaesthetic dosage of ketamine, or midazolam, interferes significantly with opiate withdrawal expression. This brings arguments in favour of a pharmacological basis underlying rapid antagonists induction in opiate dependent rats.