The speckle pattern in the image of a diffusely scattering plane surface illuminated by two mutually inclined quasi plane waves split from a common laser source gives a direct display of the coherence properties of that light source. This can be used as a simple device to check the coherence of a laser source for holographic or interferometric work. The speckle contrast is a linear function of the square modulus of the degree of coherence. This relation has been proved experimentally for coherent and for incoherent laser radiation. The main difference of the intensity distributions for coherent and incoherent illumination occurs at low intensities, which have maximum probability in the coherent and minimum probability in the incoherent case. The intensity probability distributions have been determined experimentally for two limiting cases. Within the experimental limitations they show very good agreement with the theoretical predictions. © 1971 Birkhäuser-Verlag.