The epidemiological methods of klebocin typing, antibiogram and plasmid DNA profile were evaluated using organisms isolated from a suspected epidemic of gentamicin-resistant Klebsiella pneumoniae and unrelated strains from different geographical areas as controls. The electrophoretic analysis of plasmid DNAs from Klebsiella pneumoniae showed the presence of at least one and up to as many as seven plasmids in each strain. The molecular weight of plasmid DNAs ranged from 1 to greater than 70 mega daltons. While none of the control Klebsiella pneumoniae strains showed identical plasmid profiles, 63% of the epidemic-related Klebsiella pneumoniae strains did. Klebocin typing and plasmid DNA profile gave different results for the same strains. Plasmid DNA profile was found to be a more valuable method than klebocin typing alone or klebocin typing in combination with antibiogram for differentiating epidemiologically related from unrelated isolates. Both plasmid DNA profile and klebocin typing methods were superior to antibiogram.