During and after brain ischemia, neuronal degeneration in the hippocampus is mediated largely by an excitatory amino acid, L-glutamic acid. Thus, brain ischemia injury maybe expected to be overcome by L-glutamate toxicity suppressors. In the course of our screening program for substances which protect neuronal hybridoma N18-RE-105 cells1~3) from L-glutamate toxicity, we isolated carquinostatin A4), lavanduquinocin5), and aestivophoenins A and B6). Further investigation has resulted in the isolation of 4-demethoxymichigazone(8-hydroxymethyl-2-methoxy-3H-phenoxazine-3-one) (1) from Streptomyces halstedii 2832-SVS6. We report herein the isolation, structure, and biological activities of 1.