Eighteen healthy beagle dogs of both sexes were each given 0, 2 or 4 mg/kg marbofloxacin intravenously before the subcutaneous implantation of a silicon tissue cage. Two millilitres of a suspension containing 1.3 x 104 colony forming units (CFU)/ ml of Staphylococcus intermedius were then injected into the cage 15 minutes after the intravenous injection. The dogs were clinically assessed immediately, and then two, four, eight and 24 hours after the challenge. Samples of inflammatory fluid were harvested at the same times in order to count staphylococci and to assay marbofloxacin concentrations. Blood samples were taken in order to assay plasma marbofloxacin levels. The staphylococcal counts were lower in both treated groups than in untreated dogs (P<0.01). All the clinical criteria were similar in the three groups. The concentration of marbofloxacin was similar in plasma and inflammatory fluid. Both doses were well tolerated and no adverse reactions were observed.