The majority of S. aureus strains isolated from beak-swabs and pathological processes in chicken shows coagulation of human plasma (not of bovine plasma), crystal violet-type A, hemolysinetype *4, formation of fibrinolysin, not formation of DXase and reactions with the experimental phage A1591. Because of the absence of DNase-formation and the reaction-specificity for phage A1591 we propose to designate these strains as host-specific variety gallinae of S. aureus. The strains from chicken are compared with strains of human, bovine, and ovine origin. An ecological study in a chicken farm has shown that S. aureus strains from chicken are not found in man and vice versa.The species Staphylococcus aureus can be subdivided into host-specific varieties (MEYER 1967, GRIGOROVA et al. 1976) and into biotypes (HAJEK and MARSALEK 1971). Host-specific-varieties or biotypes of S. aureus isolated from different ecological sources correspond to specific host animals and man, respectively, they show different biochemical characteristics and phage-patterns.The system of host-specific-varieties differentiates the species S. aureus into the varieties hominis, bovis, ovis, and canis and into strains which cannot be alloted to