Ciprofloxacin, a quinolone derivative of carboxylic acid, has a spectrum of antimicrobial activity that includes the Enterobacteriaceae, Staphylococcus aureus and Pseudomonas aeruginosa (1). It may therefore prove useful, alone or in combination, in the prophylaxis or treatment of infections in patients undergoing abdominal surgery. Intraperitoneal and serum levels were determined in these patients at varying times following a 100 mg intravenous dose of ciprofloxacin.