It is very critical in microbiology to determine the effectiveness of a chemical to either inhibit or kill an organism as it can help cure a disease. If the agent kills the bacteria, it is called bactericidal. If the agent inhibits the growth of bacteria, it is called bateriostatic. (Fundaments of Microbiology Lab Manual) The purpose of this experiment was to examine the effect different disinfectants and antiseptics, which are used to decrease the number of microbes, on Escherichia coli and Staphylococcus aureus. The effectiveness of the chemical agent was determined by the size of the zone of inhibition around the disc incubated on soft nutrient agar seeded with the two bacteria on separate plates. For E. coli, a gram negative organism, the zone of inhibition was the largest with Lysol (0.2mm). Next, Scope has slightly smaller zone of inhibition, 0.15mm, on the organism. Hydrogen peroxide, Wescodyne and 70 percent Ethyl Alcohol had no affect on the bacteria. Inhibition of S. aureus was exhibited by Hydrogen Peroxide (0.19mm) and Lysol (0.13mm), Hydrogen Peroxide having the largest inhibition zone. Scope, Wescodyne, and 70% Ethyl Alcohol were negative for having inhibiting capacity. From these results, it can be said that disinfectant or antiseptics are bacteria specific. They might work on one bacterium and they might not on others. For example, Scope has zone of inhibition for E. coli but not S. aureus. Also, the results show that Scope particularly inhibits the gram negative bacterium, E. coli and Hydrogen Peroxide particularly inhibits the gram positive bacterium, S. aureus. Conversely, Lysol was able to inhibit both gram negative and gram positive. Again, this characteristic illustrates the selective nature of disinfectants/antiseptics. Wescodyne used as a disinfectant in laboratory and 70% Ethyl Alcohol had no affect on either of the bacterium.