The Computer Automated Structure Evaluation (CASE) program was used to study a series of quinolone antibacterial agents for which experimental data pertaining to DNA gyrase inhibition as well as MICs against several strains of gram-positive and gram-negative bacteria are available. The result of the analysis was the automatic generation of molecular fragments relevant to the respective biological endpoints. The potential significance of these major activating-inactivating fragments to the biological activity is discussed.