The methods of measuring the space charge reduction factor for shot noise are briefly reviewed, and attention is drawn to the difficulties of making a similar measurement for flicker noise. An indirect qualitative test is described in which a triode is used both in normal manner and as a diode under retarding field conditions. Noise measurements at a high and a low frequency show that the effect of space charge on flicker noise exceeds that for shot noise. The diode results are used to estimate the value of the flicker noise reduction factor which is then seen to have a value less than the corresponding shot noise reduction factor at all current levels.