HOCl elicits comparable toxicity to MPO. A549 cells were exposed to MPO for 2 and 4 hours (A) or HOCl for 5 minutes (B) and toxicity was compared 24 hours after the exposure. MPO requires H2O2 to catalyze the formation of HOCl, therefore the glucose/glucose oxidase (GOX) system was utilized to produce H2O2. The MPO/GOX showed significant increases in toxicity at both 2 and 4 hour exposures. In comparison, HOCl alone produced a concentration dependant increase in toxicity. Roughly 750 μM HOCl exhibited similar toxicity as MPO at 2 hours. Data presented as mean ± SEM, *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001 compared to controls.