The effect of axoplasmic fluid injection on regeneration of conventionally repaired nerve was studied. Twenty New Zealand rabbits were studied in two experimental groups: immediate nerve repair (Group 1A, no axoplasm; Group 1B, axoplasm injection) and delayed nerve repair (Group 2A, no axoplasm; Group 2B, axoplasm injection group). A total of 40 sciatic nerve repairs were performed. After epineurial nerve repair, axoplasmic fluid collected from the proximal and distal nerve stumps was injected under epineurium proximally and distally to the anastomotic site. In the two control groups (immediate nerve repair and delayed nerve repair, both without axoplasm), 0.9% saline was injected in a similar way. Nerve regeneration was assessed by measuring hair and nail growth, plantar and dorsal foot temperature, muscle atrophy, and the toe spread test. In the 3- and 6-month follow-up periods, nerve samples were taken for histological evaluation. Specimens were stained with toluidine blue, and 50% of the nerve cross-section area was counted from microphotographic reconstructions. After immediate repair in Group 1, axoplasmic fluid-treated animals showed a 27% increase in the number of myelinated axons at 3 months when compared with saline-treated controls (3,768 vs. 2,962 +/- 1,921 SD). After delayed repair in Group 2, a 32% increase in myelination axon counts was detected at 3 months in axoplasm-treated animals compared with saline-injected controls (1,040 +/- 684 SD vs. 786 +/- 389 SD). In addition, a positive toe spread test result was seen at 6 months in the axoplasmic fluid-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)