A hybrid LC/MS/MS and proteomics method was developed for the assessment of multiple pesticide exposure. The methodology was based on the analysis of tryptic peptides resulting from inhibited butyrylcholinesterase (BChE) after exposure to pesticides including organophosphates (OPs) and carbamates (CBs). The primary advantage of the assay was its ability to simultaneously examine multiple pesticide exposures in a single analytical experiment. Application of tandem and MS(3) techniques provided identities of the inhibiting pesticide, confirmation and localization of the site of inhibition and relative quantification of phosphorylated peptides present in tryptic digests of equine BChE (eBChE).