Antimicrobial activities of 10-100% (wt/vol) concentrations of new honey, stored honey, heated honey, ultraviolet-exposed honey, and heated stored honey were tested against common human pathogens, including Escherichia coli, Entrobacter cloacae, Pseudomonas aeruginosa, Shigella dysenteriae, Klebsiella sp., Haemophilus influenzae, Proteus sp., Staphylococcus aureus, Streptococcus hemolyticus group B, and Candida albicans. Antimicrobial activity of honey was tested in acidic, neutral, or alkaline media. These were compared with similar concentrations of glucose in nutrient broth. Surgical wounds were made on the dorsum of mice and infected with S. aureus or Klebsiella sp. The wounds were treated with local application of honey four times a day or appropriate antibiotics and compared with control values. Bacterial conjunctivitis due to E. coli, Proteus sp., S. aureus, Klebsiella sp., and P. aeruginosa was induced in rats. Conjunctival application of honey four times a day or appropriate antibiotics was used for treatment and compared with control values. Growth of all the isolates was completely inhibited by 30-100% honey concentrations. The most sensitive microbes were E. coli, P. aeruginosa, and H. influenzae. Glucose showed less antimicrobial activity than honey, and many microbes showed positive culture even in 100% glucose. Heating to 80 degrees C for 1 hour decreased antimicrobial activity of both new and stored honey. Storage of honey for 5 years decreased its antimicrobial activity, while ultraviolet light exposure increased its activity against some of the microorganisms. Antimicrobial activity of honey was stronger in acidic media than in neutral or alkaline media. Single doses of honey used to prepare the 60% concentration in nutrient broth were bacteriocidal for P. aeruginosa and bacteriostatic for S. aureus and Klebsiella sp. during certain periods. Local application of raw honey on infected wounds reduced redness, swelling, time for complete resolution of lesion, and time for eradication of bacterial infection due to S. aureus or Klebsiella sp. Its potency was comparable to that of local antibiotics. Honey application into infective conjunctivitis reduced redness, swelling, pus discharge, and time for eradication of bacterial infections due to all the isolates tested.