Histamine release is a frequent event in the perioperative period. The reasons for its occurrence are complex; they include pseudoallergic and allergic phenomena--and probably a mixture of both. Some drugs and solvents seem to modulate histamine release induced by other drugs. Thus the terms "specific and nonspecific" or "selective and nonselective" histamine release which have their well appreciated place in experimental immunology and pharmacology should be avoided in describing histamine release responses in clinical conditions. The clinical relevance of histamine release in the perioperative period is considerable and can be compared with that of perioperative thrombosis and thromboembolism. Far too many drugs and anaesthetic and surgical procedures give increased plasma histamine levels; premedication with H1- + H2-histamine receptor antagonists is therefore recommended in patients who have a history of hypersensitivity reactions to intravenous agents; a history of atopy, who are to be given the same drug a few days later, undergo surgery with a high risk of histamine release, are more than 70 years old or are poor risk patients with perioperative cardiac, respiratory or liver failure and shock.