Class of 2012 Abstract / Specific Aims: Determine the difference in venom potency among Mohave Rattlesnakes in Cochise in Pima Counties and determine if those differences correlate to changes in clinical outcomes. Methods: Twenty-one Mohave rattlesnakes, C. s. scutulatus were collected from Arizona and New Mexico. Venom proteomes were analyzed using RP-HPLC and SDS-PAGE. The toxicity of venoms was analyzed using LD50. Health severity outcomes between two Arizona counties, Pima and Cochise, were determined by retrospective chart review of the Arizona Poison and Drug Information Center database between 2002-2009. Main Results: Six phenotypes were identified based on three venom proteins; Mojave toxin, SVMP PI and PIII, and myotoxin. Venom changed geographically from SVMP-rich to Mojave toxin-rich phenotypes from south central to southeastern Arizona. Phenotypes containing myotoxins were only found in the transitional zone between the SVMP and Mojave toxin phenotypes. Venom samples containing the largest amounts of SVMP or Mojave toxin had highest and lowest LD50s, respectively. Conclusions: There was a significant difference when comparing the presence of CNS affects between Pima and Cochise counties (p = 0.001). No significant difference was found when comparing severity number of antivenom vials administered, days spent in a health care facility or envenomation per 100,000 population. Although not part of the original data to be collected, death and intubations, were also noted. There is a 10x and 50x increased risk of death or intubations if envenomated in Cochise County.