Abstract We report the first successful collection and biochemical analysis of endoneurially enriched fluid (EEF) from sciatic nerve of control and lead-intoxicated rats using an implanted polyethylene matrix capsule and collector. The EEF protein concentration was approximately one-half that of rat serum. Protein fractionation by sodium dodecyl sulfate-pore gradient electrophoresis revealed a different protein composition for the endoneurium, EEF, and serum from the same animal. In EEF there is a complex array of protein bands with a molecular weight range of 10 4 to 2 × 10 5 of which albumin was a major constituent. Preliminary results on lead-intoxicated rats suggest that total endoneurial fluid protein may be increased during lead intoxication.