Respiratory infections with penicillin resistant pneumococci constitute an increasing health care problem. This paper describes the nosocomial spread of penicillin resistant pneumococci (PRP) on a pulmonary ward. During an eight-month period, minimal inhibitory concentrations (MICs) for penicillin and several other antibiotics were performed on all Streptococcus pneumoniae isolates that were shown to be penicillin resistant by a screening assay. The personal data and case history of all patients with penicillin resistant pneumococci were evaluated. Penicillin Resistant Pneumococci were cultured from 18 patients, 16 men (mean age 74 +/- 8 yrs) and 2 women (aged 54 and 60 yrs). Chronic obstructive pulmonary disease was diagnosed in 16 patients, 10 of which had an additional underlying disease (2 diabetes mellitus, 2 heart failure, 2 malignancy). Prior to culture of Penicillin Resistant Pneumococci, 11 out of 18 patients were treated with antibiotics, a beta-lactam in most instances. Ten out of 18 patients died during or shortly after hospitalization. The death of one patient seems to be directly related to infection with Penicillin Resistant Pneumococci. The five Penicillin Resistant Pneumococci isolates available for serotyping were all type 9. The minimal inhibitory concentrations for penicillin varied from 0.5 to 2.0 mg.l-1. High minimal inhibitory concentrations were also noted for cefixime (all over 4.0 mg.l-1) and ceftriaxone (0.5-1.0 mg.l-1). It is concluded that penicillin resistant pneumococci can spread rapidly among old and debilitated patients. Thus, patients with this infection should be barrier nursed.