The guidelines used in Dutch hospitals for the treatment of pneumonia as described in antibiotic formularies are described. A total of 42 formularies were examined. Amoxycillin was the most frequently used agent in the treatment of community-acquired pneumonia and a wide variety of drugs was used for the treatment of nosocomial pneumonia, of which cefuroxime, alone or in combination with an aminoglycoside, was used most often. Benzylpenicillin was the most frequently used drug in community-acquired aspiration pneumonia; this drug, in combination with an aminoglycoside, was also the drug of choice in hospital-acquired aspiration pneumonia. Treatment of pneumonias with known or presumed pathogens was also surveyed and the most usual drugs of choice were benzylpenicillin for pneumococci, flucloxacillin for staphylococci, amoxycillin for Haemophilus influenzae , cefuroxime for Enterobacteriaceae (cefuroxime), cotrimoxazole for Pneumocystis carinii , doxy-cycline and erythromycin for Mycoplasma pneumoniae and erythromycin for Legionella pneumophila . Relatively wide variations in dosage guidelines were observed for benzylpenicillin and amoxycillin. Only a few formularies gave guidelines for the duration of treatment.