Mastitis is a serious problem for sheep and rabbit farms, Staphylococcus aureus being the main causal agent. Fifty strains of S. aureus isolated from sheep and rabbits from farms located in diverse geographical regions of Spain were studied. Their resistance pattern and plasmid profile was related to the pulsotypes obtained by pulsed-field gel electrophoresis (PFGE). The results showed great heterogeneity in staphylococci isolated from sheep, both in pulse-type and plasmid profile. We found in addition, antibiotic-resistant strains and aminoglycoside-modifying enzyme (AGMEs) producer strains. The genotypes corresponding to staphylococci isolated from rabbits were less heterogeneous, although they also could be subdivided by plasmid profile and resistance patterns. Resistance to antibiotics such as methicillin or AGMEs production could indicate possible human origin of the strains or a possible source of resistant strains for human beings. © 2003 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.