Brain tissue was analyzed for acetylcholinesterase (AChE) activity from 24 American pronghorn antelope (Antilocapra americana) collected on the US Army Dugway Proving Ground (DPG) (latitude 40°13' 52" N, longitude 112°45' 01" W), Tooele County, Utah. Pronghorn antelope from DPG were evaluated against 26 pronghorn antelope collected in Wyoming. The mean AChE activity was significantly greater (P < 0.001) in the Wyoming control group (4.612 ± 0.193 μM/gm brain tissue/min) relative to DPG (4.032 ± 0.621 μM/gm brain tissue/min). The DPG database exhibited a fourfold greater coefficient of variation, a tenfold greater variance, and a threefold increase in the standard deviation when compared to control AChE activity. Furthermore, the 95% confidence interval for the control and for the DPG data were not overlapping; the entire control data set was greater than the mean DPG AChE activity. A post hoc sequential Bonferroni statistical procedure showed two significantly (P < 0.001) distinct subsets in the DPG data. Mean DPG Subset I AChE activity (4.528 ± 0.347 μM/gm brain tissue/min) was indistinct from the mean control AChE value (4.612 ± 0.193 μM/gm brain tissue/min). The mean DPG Subset II AChE activity (3.537 ± 0.387 μM/gm brain tissue/min) differed significantly (P < 0.001) from the mean control AChE activity. The sum of resulting α values from the multiple statistical tests did not exceed the selected α value of P < 0.05, validating the post hoc sequential Bonferroni statistical procedure. Pronghorn antelope represented by Subset II, experienced a 23.3% mean loss of AChE activity suggesting sub-lethal organophosphate (OP) exposure rather than a low level chronic environmental influence was experienced by a population subset of the DPG pronghorn antelope herd. The origin of the DPG sublethal OP exposure and its long-term effects are speculative.