Light emission has been obtained from extracts of acetone powders of Collybia velutipes or Armillaria mellea. A hot-water extract, presumably luciferin, when mixed with a cold-water extract, presumably luciferase, will emit light. The intensity and total amount of light emitted by these extracts can be greatly increased by the addition of either reduced triphosphopy-ridine nucleotide or reduced diphosphopyridine nucleotide. Oxygen is also required for light emission.