Nine cases of Clostridium difficile (CD) infection were observed in the period of six months at a nursing home. Eight of them occurred during or after antibiotic treatment. Levofloxacin was used alone in three cases and in combination with another antibiotic in three other cases. CD infection occurred with other antibiotics in two cases. In one case, CD infection occurred without any antibiotic treatment. It is generally accepted that quinolones rarely cause CD infection. Levofloxacin, a new antibiotic of a quinolone group, appears to be an exception. Considering the endemic level of CD infection and the high mortality and morbidity among elderly residents in the long-term care facilities, CD infection should be considered one of the major adverse effects of antibiotic therapy. Physicians are cautioned to prescribe antibiotics judiciously and to anticipate CD infection during and after antibiotic treatment.