Male Sprague-Dawley rats (200 g) were injected subcutaneously with soman, a potent neuronal acetylcholinesterase (AChE) inhibitor, at doses of 0.5, 0.8 and 1.0 LD50 (1 LD50 = 135 micrograms/kg) before decapitation at 1 and 24 h post-exposure. Correlative data were obtained on the severity of brain AChE inactivation and physicochemical changes in nuclear chromatin of cerebrocortical (layer V) and striatal neurons using Feulgen-DNA (F-DNA) cytophotometry and ocular filar micrometry. Decreased lability of neurons to F-DNA acid hydrolysis (reduced F-DNA yield), nuclear shrinkage and chromatin aggregation (decreased chromophore area) were used as indices of suppression of genomic template activity; conversely, increases in F-DNA yield and chromophore area signify enhanced neuroexcitation. At 1 hr post-soman there was a dose-dependent inactivation of AChE with a moderate increase in chromatin activation, i.e., nuclear hypertrophy and chromatin dispersion. At 24 hr post-soman there was a partial restoration of AChE activity, notably in striatal neurons, with a suppression in chromatin template activity. These data indicate that actions of soman on neuronal functioning are time-dependent. The absence of any dose-related neuronal chromatin changes may signify existence of non-cholinergic mediated events.