An outbreak of penicillin-resistant Streptococcus pneumoniae (PRSP) infections occurred in our hospital between January and May of 1993. Nine patients with infections/colonizations were located in 3 multiplebed rooms on an internal medicine ward. Two of the 9 patients developed pneumonia, 3 developed acute bronchitis, and 4 patients demonstrated colonization in the respiratory tract. Only 1 case of acute bronchitis was confirmed as a community-acquired infection, while the others were considered nosocomial infections, subsequently shown to be caused by at least 2 different bacterial strains. The cases of pneumonia were thought to be cross-infections transmitted by droplets. All patients with either pneumonia or bronchitis were cured by the administration of various antibiotics, including imipenem and ofloxacin. Of the 4 colonization cases, 3 patients were treated with antibiotics and the organisms successfully eradicated. Although all 5 patients with infections were cured, it is important to be attentive to the emergence of PRSP infections, as there are potential difficulties in the treatment of this organism.