Susceptibility testing against gram-positive and gram-negative bacteria was carried out using fresh aqueous, heated aqueous and dried powder solutions of garlic. Pseudomonas aeruginosa was not inhibited by the garlic extract. Dried garlic powder showed comparable antimicrobial properties against Staphylococcus aureus and Salmonella typhimurium as fresh unheated garlic extract. However, when the aqueous garlic extract was subjected to heating for 20 minutes, its antimicrobial property was significantly reduced. The disk diffusion technique appears to be more reliable for susceptibility testing than the agar-gel diffusion technique, since the disk diffusion test correlates well with the results of the Minimum Inhibitory Concentration (MIC). Our results show that garlic disks of 6.25 mg should be used for susceptibility testing. Zone sizes of 29 mm and above should indicate susceptibility for S. aureus.