Summary Cultures of Staphylococcus aureus from 36 food-poisoning incidents in Great Britain during the period 1961–69 were examined for their ability to produce enterotoxins A, B, C and, in some tests, enterotoxin D. Enterotoxin was produced by means of a sac-culture technique and detected serologically by the slide gel double-diffusion method. Enterotoxins A, B, C, or D were demonstrated from strains from 33 of 36 incidents (92 per cent.) and in some instances two enterotoxins were produced by one strain; enterotoxin A was the predominant type. Strains from 34 of 36 (94 per cent.) were lysed by phages of group III and in 13 of these incidents reactions were also obtained with phages of group I. Of 36 cultures of Staph. aureus isolated from a range of routine food samples not associated with food-poisoning incidents, 13 produced enterotoxins A, B, or C.