1. Staphylococcus aureus was able to colonise the surface of chicks as young as 1 d old. 2. The organism was detected in a hatchery particularly in the debris from the hatchers and on the working surfaces at the sexing and vaccination areas. 3. The degree of surface colonisation of chicks and pullets was low during rearing but rose to a maximum at mid-lay (50 weeks) when the organism was readily detectable on almost all hens. 4. Strains of Staphylococcus aureus were characterised by phage-typing and cultural characteristics and found to belong predominantly to poultry phage group B2 of Gibbs et al. (1978a). 5. A detailed description of poultry phage group B2 strains is presented; strains of this type can be considered as a second "live-bird" ecovar when compared with Staph. aureus var. gallinae of Witte et al. (1977).

A set of phages has been isolated from strains of Staphylococcus aureus, non‐typable with the International (human) phage set, recovered from processed poultry. This set of phages could distinguish three main groups of strains, and biochemical tests confirmed these divisions, members of each group exhibiting characteristics of both ‘human’and ‘animal’strains. A high proportion of strains from all three phage groups was enterotoxigenic.

A set of phages previously isolated from poultry strains of Staphylococcus aureus was used to type such isolates from poultry before, during and after processing in a poultry plant. Certain poultry phage types were found to be associated with the live birds rather than the processed carcases. Strains lysed by phages from this group may represent a specific ‘poultry’biotype. A site of cross‐contamination within the plant was discovered.

1. Eighty per cent of poultry strains of Staphylococcus aureus tested from French, Belgian, English, West German, Japanese and Argentinian sources were typable using a set of typing phages isolated in this laboratory. Strains from Bulgaria, however, with few exceptions were not typable with this phage set. 2. Strains isolated from lesions generally resembled those from apparently healthy poultry. 3. The existence of two distinct Staph. aureus biotypes on poultry was confirmed by isolates from six of the countries; one of these biotypes closely resembled Staph. aureus variety gallinae as described by Witte et al. (1977).