A process allowing measuring of viscosity of a culture medium of microorganisms including a) immersing at least one particle that is charged electrically, is magnetic or can be magnetized or covered with at least one magnetic or magnetizable layer in the culture, b) subjecting the culture to an electrical, magnetic or electromagnetic field in such a manner as to put the particle in motion, and c) optically detecting the degree of freedom of motion of the particle in the culture without a scanning microscope.