organophosphorus compounds which, after acute administration, inhibit neurotoxic esterase (nte) by > or = 65 and undergo a subsequent 'aging' reaction, produce a delayed neuropathy characterized by degeneration of large and long nerve fibers. the present studies examine in detail the nte-inhibiting properties of triphenyl phosphite (tpp), a plasticizer which produces ataxia and degeneration of the spinal cord in animals. a neurotoxic dosing regimen (1184 mg/kg/week, sc, for 2 weeks) inhibited both brain and spinal cord nte (< or = 40) only marginally 4 and 48 hr postdosing by contrast, tpp was shown in vitro to be a potent inhibitor of rat brain nte relative to mipafox or diisopropyl phosphorofluoridate preincubation of 10 micromolar tpp in buffer (37 deg c) resulted in a time-dependent loss of tpp's ability to inhibit nte. in summary, tpp is a powerful nte inhibitor in vitro, but only a marginal nte inhibitor after in vivo administration. these results raise questions as to the causal events mediating tpp-induced neuropathy in the rat (copyright (c) 1987 academic press, inc.)