A nosocomial outbreak of acute bronchitis due to amoxycillin-resistant, non-typable Haemophilus influenzae occurred in a 23-bed unit, housing patients with respiratory disorders. Within a period of one month, 13 patients and two, previously healthy, members of staff were affected. The isolates were studied for strain relatedness by serotyping, biotyping and major outer membrane protein (MOMP) profiles after SDS-polyacrylamide gel electrophoresis; 13 of the isolates belonged to the same biotype and MOMP type, indicating cross-infection. Routine throat cultures of all patients and personnel were undertaken. To stop the epidemic, patients and nurses positive for amoxycillin-resistant H. influenzae were isolated or sent home and, if symptomatic, were treated with co-trimoxazole. We stress the importance of early intervention when amoxycillin-resistant H. influenzae strains occur in a ward.