There is a growing concern about rational prescribing of antibiotics. That is why a secondary analysis of prescribing antibiotics in upper respiratory tract infections has been conducted by means of a nationwide study of morbidity and interventions in The Netherlands. The mean percentage of antibiotic prescriptions varied from about 20% for acute otitis media and acute upper respiratory tract infections to about 70% for sinusitis and tonsillitis. Only attitude--toward prescribing antibiotics in sore throat--and years of settlement were important predictor variables. The other characteristics studied--type of practice, list size, frequency of use of Het Farmacotherapeutisch Kompas, containing national pharmacotherapeutical guidelines, and urbanization level were not. The importance of attitude, however, was less for general practitioners who went into practice after 1975. This means that the influence of a personal characteristic as attitude might have become less influential since the introduction of vocational training for general practice.