Abstract: A laboratory hood has a housing that is horizontally elongated and that is provided with an exhaust that withdraws gas from inside the housing through the back wall thereof. A horizontally elongated diffuser chamber of the same length as the housing is subdivided by a horizontal partition into a pair of vertically spaced compartments communicating through a full-length slot that is formed by the partition. An intake blower pressurizes the top compartment through a relatively narrow conduit and a wide conduit whose width is equal to the full length of the chamber and housing extends between the lower compartment and the top wall of the housing so that air fed to the upper compartment can diffuse through the slot and then pass down through the wide conduit to issue as a broad curtain in the hood. The front wall of the conduit is planar to direct a portion of its air straight down and the rear wall of the conduit is downwardly and forwardly convexly curved to direct part of the air backwardly.