Abstract: A method and apparatus for operating a rotary retort heat treating furnace involves incorporating an outlet for withdrawing furnace atmosphere from the retort above the axis of rotation and conveying the withdrawn gas remotely form measurement at the temperature conditions where the heat treatment process occurs. The method and apparatus also involves introducing the treatment atmosphere and sampling the atmosphere at a point adjacent the retort product discharge outlet. The use of the above-center outlet and remote probe eliminate structural problems encountered in prior art attempts to measure and control the furnace atmosphere in rotary retort furnaces.