Measurements are reported on noise in field emission vavuum diodes. In some devices the noise spectrum is of the type Ieq = (Ia + A/fα), whereas in other devices is of the type Ieq = (Ia 1 2 + A 1 2/fα/2)2; in most cases α is close to 3 2. The first type of noise can be interpreted as the result of two independent noise sources, excess noise and shot noise, speculations are made about the second typw of noise. In many cases the excess noise spectrum is levelling off below 10 cycles. The excess noise is interpreted in terms of work function fluctuations governed by a diffusion of atoms over the surface. This gives a 1/f 3 2 spectrum at high frequencies whereas the spectrum levels off at low frequencies. The experimental turnover frequency agrees roughly with the theoretical predictions. The theory can also explain the temperature dependence of the field emission excess noise found by Kleint.