Exogenous myelin- or axolemma-enriched fractions were assessed for the ability to inhibit biochemical and morphological expressions of reactive gliosis in rat optic nerve. Elvax pellets containing exogenous myelin, axolemma, whole-brain homogenate, liver, or red cell extracts or no homogenate were inserted into a dural slit in distal regions of crushed optic nerve. Biochemical and morphological expressions of reactive gliosis were assessed at 7 or 14 days postoperatively. Post-traumatic elevations in lactic dehydrogenase activity normally seen at 7 days postoperatively were prevented by placement of Elvax pellets containing myelin or axolemmal fractions into the optic nerve. Morphological analyses indicated an inhibition of post-traumatic elevations in glial cell numbers, surface area, and nuclear size at the 14-day time point. Exposure of the axolemmal fraction to heat or trypsin inactivated its ability to modulate reactive gliotic changes. Myelin fractions were trypsin-sensitive, but not heat-sensitive. In contrast, Elvax pellets containing whole-brain tissue homogenates or liver and red cell membranes had no significant effects on post-traumatic glial changes relative to preparations in which homogenate-free pellets were used.