The possible role of ganglioside GM₁ in the modulation of the effects of nerve growth factor (NGF) on nerve regeneration was investigated in 30 rats after 3 mm of their 60 sciatic nerves were crushed. The rats were equally divided into 2 groups and the animals of one group were treated with an injection of 2.1 μl solution of 1 μg NGF to the crushed sites and those of the other group with an injection of 2.1 μl solution of 1 μl of NGF and 10 μl of GM₁. Five rats of each group were killed on days 12. 28 and 56 after injection respectively and 10 mm of the sciatic nerve distal to the crushed sites was resected and prepared for various determinations and pathological study. It was found microscopically that the regenerated nerve consisted of myelinated and unmyelinated fibers. Schwann's cells, capillaries and collagen fibers. Substantially more regenerated myelinated fibers (RMFs) on the 12th day and significantly larger diameter of RMGs on the 28th and 56th days were demonstrated in the NGF-GM₁ treated group than in the NGF treated group. In addition, larger area occupied by the RMFs of the cross-sectional area of the nerve was shown in the NGF-GM₁ treated group in the whole observation period. These findings confirm further that GM₁ does promote the NGF effects on nerve regeneration.