Through evaluation of serum and plasma buterylcholinesterase (BChE) and brain acetylcholinesterase (AChE) activity, we investigated the possibility of the involvement of an acute organophosphate toxicosis in the pathogenesis of ongoing annual outbreaks of paresis and paralysis that in some cases progress to death, in endangered Western Australian Carnaby's cockatoos (Zanda latirostris). The condition, named Carnaby's hindlimb paralysis syndrome (CHiPS), was first described in 2012. Following initial investigations involving clinical, epidemiologic, toxicologic, gross necropsy, and histologic evaluation, a toxic etiology, specifically an organophosphate toxicosis, was considered most likely. The study aimed to validate the BChE assay for use in serum and plasma in Carnaby's cockatoos. This study found no evidence of changes in serum or plasma BChE or brain AChE that indicate an acute organophosphate toxicosis as the cause of CHiPS. Although these results render an acute organophosphate toxicosis unlikely, an organophosphate-induced delayed neuropathy has not been ruled out. Based on the results from the BChE validation study, the authors can recommend this assay for the evaluation of BChE measurement in plasma and serum from Carnaby's cockatoos with results showing excellent accuracy and precision.