The authors report treatment of eighteen haematologic patients (twelve male, six female, age between 21 and 78 years), suffering from upper respiratory tract (ten patients) and/or lower urinary tract (eight patients) infections caused by Gram-negative germs, with a combination of ciprofloxacin-azlocillin in the ratio 1:10. Before treatment, the Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Fractional Inhibitory Concentration (FIC) index of Gram-negative isolates from patients for the ciprofloxacin-azlocillin combination were evaluated. The in vitro experiments revealed a synergistic activity of the combination for 85% of isolates, while at the same concentration ciprofloxacin alone was 100% effective, and azlocillin alone was 50% effective. The combination was administered to patients as follows: ciprofloxacin: 750 mg "per os" every 12 h; azlocillin 5 g intravenously every 8 h for a therapeutic cycle of 8 days. Seventeen of the eighteen patients that were treated with the combination showed complete eradication of the causative pathogen, sixteen of the eighteen patients recovered fully, whereas the other two showed significant improvements. The tolerability of the combination was excellent in seventeen patients and only one patient developed symptoms of mild gastric intolerance. The results presented here warrant further interest in studies of this antibiotic combination.