Eight coagulase-negative, oxidase-negative and novobiocin-susceptible staphylococcal strains were isolated from the gastrointestinal tracts of South American squirrel monkeys (Saimiri sciureus L.). These strains were differentiated from known staphylococcal species on the basis of 16S rRNA gene and hsp60 gene sequencing, and from the most closely related species by using DNA-DNA hybridization, ribotyping, whole-cell protein profiles and biotyping. Phylogenetic analysis based on 16S rRNA gene sequences confirmed that these strains are members of the Staphylococcus aureus species group (99 % similarity) but are biochemically similar to Staphylococcus piscifermentans, from which they can be phenotypically distinguished by resistance to polymyxin B, acid production from D-mannitol, the inability to hydrolyse aesculin and DNA and the absence of a-glucosidase. On the basis of these analyses, a novel species of the genus Staphylococcus is described, for which the name Staphylococcus simiae sp. nov. is proposed, with CCM 7213 T (=LMG 22723 T ) as the type strain.Staphylococci are among the most widespread of the pathogenic and opportunistic pathogenic bacteria (Kloos et al., 1992). At present, 36 staphylococcal species are known: nine of them include two subspecies, and one of them includes three subspecies (Garrity et al., 2004;Spergser et al., 2003;Place et al., 2003; Švec et al., 2004). Several Staphylococcus species have been isolated from non-human primates and in some cases were associated with illness and mortality, particularly in newly imported animals (Padovan & Cantrell, 1983;Crouch et al., 1984;Stasilevich et al., 1986). An unnamed coagulase-negative and novobiocin-resistant 'Staphylococcus sp. 5' isolated from skin of squirrel monkeys has been reported previously by Kloos et al. (1976). During an outbreak of diarrhoeal disease in squirrel monkeys in a zoo in Olomouc, Czech Republic, staphylococcal strains with atypical features were isolated from both ill and healthy animals. The South American squirrel monkey (Saimiri sciureus L.) is an arboreal, small-sized, non-human primate from equatorial South America; it has always been a common sight in zoos, and laboratory-bred squirrel monkeys have long been used as an animal model in various fields of biomedical research (Rosenblum & Coe, 1985). (Freney et al., 1999; Pantů ček et al., 1999;Mannerová et al., 2003). Additional biochemical profile data were obtained by using the ID32 Staph, API Staph and API ZYM systems (bioMérieux). Susceptibility to other antibiotics was determined on Mueller-Hinton agar (Oxoid) by using a standard diffusion technique with a standard set of antibiotic discs for staphylococci (Oxoid).The characteristics of the novel isolates are summarized in the species description below. The squirrel monkey strains are phenotypically close to S. piscifermentans (Tanasupawat et al., 1992; Pantů ček et al., 1999) but differ from the latter in terms of the following biochemical characteristics: aesculin hydrolysis, DNA hydrolysis, a-and b-glucosid...