Effects of malonylginsenoside Rb1 (GRb1-m) isolated from dried root of Panax ginseng C. A. Meyer (Araliaceae) on neuronal survival and neurite outgrowth were compared with those of ginsenoside Rb1 (GRb1) using organ culture of chick embryonic dorsal root ganglia (DRG) and cell culture of DRG neurons. In the organ culture, nerve growth factor (NGF) showed neurite outgrowth promoting effect. GRb1-m (30 microM) significantly potentiated this NGF-induced neurite outgrowth with similar potency to that of GRb1 (30 microM). Low density cell culture of DRG neurons was employed to minimize the contribution of contaminating non-neuronal cells. NGF (10 ng/ml) prolonged duration of neuronal survival. Neither GRb1-m nor GRb1 (1-30 microM) changed the prolongation effect of NGF, nor did NGF show a significant effect on the neurite elongation and re-elongation after axotomy by laser beam irradiation. However, GRb1-m (10 microM) potentiated initial neurite elongation when co-treated with NGF. In the process of re-elongation of neurites, GRb1-m (1, 30 microM) also promoted it in the presence of NGF. These results suggest, first, that GRb1-m potentiates NGF-induced neurite outgrowth of chick embryonic DRGs and DRG neurons, but behaves in a slightly different manner from GRb1, and, second, that the effects of the two saponins may work primarily on neurons causing the potentiation of NGF-induced neurite outgrowth.