This study sought to determine the levels of blood contamination found in and/or on used dental anesthetic cartridges and to measure antibacterial effects after exposure to a local anesthetic solution. The study analyzed a total of 1000 used cartridges from an oral surgery clinic, containing 1 of 3 anesthetic types. Blood testing included visual observations (using a dissecting microscope) and chemical analyses. From each cartridge, either 0.5 ml of residual anesthetic solution or a combination of anesthetic solution plus added saline was removed. Using reagent strip dipsticks, the solutions were analyzed for minute amounts of blood. Visual examinations were scored on a positive or negative scale. In addition, 4 types of bacteria were mixed with lidocaine or phosphate buffered saline (PBS) for up to 30 days, and viable cell counts decreases were measured for the 2 solutions. A majority of the cartridges evaluated contained lidocaine, and while only 7 of the 1000 cartridges examined contained visible blood, the reagent strips detected blood in more than 76% of all cartridges. Lidocaine and PBS produced similar bacterial death rates. The authors concluded that blood contamination levels in the absence of pronounced antibacterial activity indicate that dental anesthetic cartridges could be considered a potential type of regulated medical waste.