The invention relates to a method for observing a sample (12), the sample (12) comprising a set of organisms (14), a solid substrate (16) supporting the set of organisms (14). The method being characterized in that the method includes steps for illuminating at least one portion of the sample (12) with a light beam, for acquiring a first diffraction pattern corresponding to an image of waves from the diffraction of the light beam by at least one portion of the set of organisms (14), for acquiring a second diffraction pattern corresponding to an image of waves from the diffraction of the light beam by at least one portion of the sample (12), for comparing the second diffraction pattern with the first diffraction pattern, for determining at least one characteristic relating to the set of organisms (14) from the result of the comparison step.