Carageenans are a group of high molecular weight sulphated polygalactans which find extensive use in the food industry as thickening, gelling and protein‐suspending agents. Although there is no evidence to suggest that the persorption of small amounts of carageenans across the intestinal barrier poses an acute toxic hazard, they are known to be biologically active in a number of physiological systems and extended oral administration in laboratory animals has been shown to modify bothin vivoandin vitroimmune competence. Whereas this effect could be attributed to carrageenan having a selective toxic effect on antigen‐processing macrophages, additional studies suggest that macrophages can also influence immune responses by the timed release of immunoregulatory mediators. Evidence in support of this comes fromin vitrostudies which demonstrate that carrageenan‐treated macrophages can, depending on conditions and time of administration, release either stimulatory or inhibitory factors. The former is known to be the immunostimulatory agent interleukin 1 (IL‐1). The inhibitory factor, which is produced at an early stage following exposure to non‐toxic doses of carrageenans, has yet to be formally identified but it is believed to be a prostaglandin because of its specific mode of action and short biological half‐life.