Abstract: A combustor for a gas turbine is shown having a catalytic reactor element to promote low temperature combustion of the fuel. An air-fuel premix chamber is provided in the upstream end of the combustor arrangement to produce a mixture which is substantially uniform throughout a plane transverse to the direction of flow of the mixture just prior to the catalytic element. The premix chamber comprises a short cylindrical member of less diameter than the shell of the combustor and closed at the upstream end, with the opposite end discharging directly to the catalytic element. The upstream portion of the walls of the cylinder contain apertures so that the air and fuel introduced into the upstream end of the combustor must flow axially into the annular space between the shell and the chamber, then the flow is abruptly changed to a somewhat radial component to enter the apertures and then the flow is again abruptly changed to an axial direction to enter the catalytic reactor.