Development of biomarkers of human exposures to organophosphorus compounds OPCs and their quantification is a vital component of a system of prediction and early diagnostics of OPC-induced diseases. Our study was focused on investigation of esterase status as a complex biomarker of exposure to OPCs and an aid in accurate diagnosis. We suggest that this complex biomarker should be more effective and informative than standard assays of plasma butyrylcholinesterase (BChE), erythrocyte acetylcholinesterase (RBC AChE), and lymphocyte neuropathy target esterase (NTE). It will help: 1) to assess an exposure as such and to confirm the nonexposure of individuals suspected to have been exposed; 2) to determine if the exposure was to agents expected to produce acute and/or delayed neurotoxicity; 3) to perform dosimetry of the exposure, which provides valuable information for medical treatment. To confirm this hypothesis, we have examined the changes in activity of blood AChE, NTE, BChE and carboxylesterase (CaE) 1 h after i.p. administration of increasing doses of three OPCs with different esterase profiles: the known neuropathic compound O,O-dipropyl-O-dichlorovinyl phosphate (C3H 7O)2P(O)OCH=CCl2 (diPr-DClVP) as the control compound and two model dialkylphosphates (C2H5O)2P(O)OCH(CF3)2 (diEt-PFP) and (C4H9O)2P(O)OCH(CF3)2 (diBu-PFP). The esterases assay was performed in hemolysed blood by spectrophotometric (AChE, BChE, CaE) and biosensor (NTE) methods. Analysis of the obtained dose-dependences for blood esterases inhibition showed that blood BChE and CaE were the most sensitive biomarkers, allowing detection of low doses. Inhibition of blood NTE and AChE can be used to assess the likelihood that an exposure to OPC would produce cholinergic and/or delayed neuropathic effects.