Ketamine, when used as a mono-anaesthetic, does not appear to induce surgical anaesthesia in the pig. The addition of other drugs such as opioids, benzodiazepines and alpha 2-adrenergic agonists deepens anaesthesia and enables major surgery to be performed. A decision-tree for the rational use of ketamine for both short and long-term anaesthesia in the pig under three different levels of procedure severity is presented.