Abstract: A powder level measurement probe is described for use in a polypropylene gas phase reactor. The apparatus comprises a support tube which extends downwardly from the upper end of the reactor and which has a non-metallic powder probe holder mounted on the lower end thereof. The holder is provided with upper and lower recessed areas formed therein. A metal proximity sensor is positioned in the upper recessed area and is operatively connected to a signal device such as a light or the like which is positioned remote from the reactor. A metal plate is movably positioned in the lower recessed area of the holder and has a probe secured thereto which extends downwardly therefrom which is adapted to be engaged by the powder within the reactor. Movement of the probe by the powder causes the metal proximity sensor to be activated which in turn activates the signal device connected thereto.