OBJECTIVE: To explore the mechanism of tissue specificity of neurotropism in peripheral nerve regeneration, we investigated the biological characteristics of the nerve regeneration conditioned fluids(NRCF) on motoneuron of SD rats cultured in vitro. METHODS: Silicon chambers were sutured respectively to the distal stumps of motorial branch of femoral nerve and saphenous nerve to collect NRCF, namely MD-NRCF and SD-NRCF. The rats cortex motoneuron were divided into 4 groups and cocultured with MD-NRCF, SD-NRCF, b-FGF and serum-free medium respectively. The cultured cells were photoed under phase-contrast microscope, their longest neurites and cell-body areas were measured by cell image processing computer system. MTT automated colorimetric microassay was also adopted to quantify the activation of cultured motoneurons in each group. RESULTS: Cells of MD-NRCF group had longer neurites than those of the other three groups, and their activation was also superior to those of the other groups. CONCLUSION: The results suggest that MD-NRCF has more significantly neurite-promoting and neurobiological effects on motoneuron than SD-NRCF and b-FGF.