Biofilm is an example of bacterial group behavior. We investigated the effect of N-acetylcysteine (NAC) alone and in combination with ciprofloxacin on Pseudomonas aeruginosa biofilm formation. Four groups (each contains six molds) of standardized bone cement molds were infected. NAC, ciprofloxacin each alone, and NAC/ciprofloxacin combination were evaluated in point of inhibiting and eradicating biofilm capacity using microbiological and electron microscopical evaluation techniques. Microbial counts and electron microscopical observations showed that the effect of NAC and ciprofloxacin combination on biofilm formation in bone cement is valuable. NAC enhances the beneficial effect of ciprofloxacin when used in combination with it in bone cement. SCANNING 38:766-770, 2016. (c) 2016 Wiley Periodicals, Inc.