Altogether 55 S. aureus strains were isolated from the nose and skin of 2 monkey species (Cercopithecus sabaeus and Macaca fascicularis). The strains were studied in 19 biological tests. 45 of these strains were found to differ in their biological properties from the ecological S. aureus variants described in literature. Of these grounds the strains were classified with the new ecovar simiae comprising 2 subvariants. The strains of the ecovar simiae coagulated human plasma, did not coagulate bovine plasma, formed type A/B colonies on a medium containing crystalline violet, required longer time to ferment mannitol (4-5 days), possessed DNase, were sensitive to "human" and resistant to "bovine" phages. The cultures of subvariant 1 produced fibrinolysin and caused type A hemolysis, the strains of subvariant 2 has no fibrinolysin and caused types B and C hemolysis.