Several substances which are secreted after surgery are thought to contribute to immune suppression in general and NK cell dysfunction in particular. These include prostaglandins, catecholamines, steroids and endorphins, have all been shown to suppress several immunological functions in vitro (1). Animal studies have shown that administration of prostaglandins and catecholamines to rats suppresses NK cell activity in vivo, in association with elevated susceptibility to metastases 4-6).