Low-frequency noise measurements are shown to provide a convenient and reasonably accurate (±10 per cent) means of measuring r\´_{b}. Their application to the measurement of the factor

in the junction law

is also described, though the values of

obtained from noise measurements do not check accurately with the values of

determined by other methods. Experimental determinations of the variation of low-frequency noise figure with emitter-bias current are also presented for several transistor types. The observed behavior suggests that the principal source of

noise in low-noise transistors may be in the emitter-base transition region instead of on the base surfaces where it is placed in presently accepted noise models.