We identified S9940, a novel microbial metabolite from Streptomyces spp., to inhibit the release of neurotransmitter from PC12 cells. S9940 is an inhibitor of trifiated norepinephrine ([$^{3}H$]-NE) release in high $K^+$ buffer solution containing ionomycin, indicating that S9940 inhibits neurotransmitter release after the influx of $Ca^{2+}$ ions. We also examined the effect of S9940 on $eta-glucuronidase$ release from guinea pig neurophils and the effect on the neurite extension of PC12 cells and rat hippocampal neurons. As a result, S9940 inhibited $eta-glucuronidase$ release: when treated with $5{mu}g/ml$ of S9940, which prevented [$^{3}H$]-NE release, the inhibition of neurite extension for both PC12 cells and rat hippocampal neurons was observed.