In the submitted paper the authors focused their attention on the characteristics of Gram-negative bacteria with a marginal sensitivity and resistance to ofloxacin (MIC > or = 2 mg.l-1) isolated from clinical materials in the Olomouc Faculty Hospital. They give an account of their sensitivity (based on assessment of the minimal inhibitory concentration-MIC) to 20 other antibiotics and chemotherapeutic agents and the percentage ratio of different species according to department, clinical material and diagnosis.