The interaction of dialkyl (alpha-carbometoxy-beta,beta,beta-trifluoroethyl) phosphates (RO)2P(O) . OCH(CF3)COOMe (R = Me, Et, Pr, Pri, Bu, Bui, Am, Hex) (I-VIII) with human erythrocyte acetylcholinesterase, horse serum butyrylcholinesterase, pig liver carboxylesterase was studied and acute toxicity in mice was estimated. Compounds (I)-(VIII) were not hydrolyzed by carboxylesterase, slowly and irreversibly inhibited acetylcholinesterase (kII = 10(2)-10(4) M-1 X min-1) and more efficiently inhibited butyrylcholinesterase and carboxylesterase (kII = 10(3)-10(7) M-1 X min-1). The structure--antienzymatic activity relationships were investigated. With increasing of hydrophobicity of alkoxy groups, antienzymatic activity to butyrylcholinesterase and carboxylesterase ("sites of loss") rises equally and more significantly, than antiacetylcholinesterase activity (delta lg kII 1.0 and 2.4 for R = CH3 and C5H11 resp.). Branching at the alpha-position of alkoxy groups leads to sharp reducing of acetylcholinesterase and butyrylcholinesterase inhibition constants, the carboxylesterase inhibition mechanism becoming reversible. Multiple regression analysis (the Kubinyi model) showed that influence of steric hindrances is revealed at the phosphorylation stage. It was found that phosphates (I)-(VIII) possess low acute toxicity in mice (900-2000 mg/kg). The toxicity of this homologous series appears to be independent of the hydrophobicity. Role of esterases in toxicological effect of compounds (I)-(VIII) is discussed.