Fex-M3d was a poisonous gas. It entered a victim's bloodstream after being inhaled and bound itself to neuro-receptors, preventing nerves from sending signals and thereby causing the individual to suffocate as the diaphragm would cease to contract and expand. It did not affect species who did not depend on respiration, such as the Lungless Gand. Fex-M3d was used to guard Imperial computer complexes on Coruscant.