The present paper aims at describing systematically the theory of thought-styles and thought-collectives of Polish microbiologist, Ludwik Fleck. The paper describes its starting point: case study of so-called Wasserman test. In what follows, Fleck’s theory is presented at first in the light of Structure of Scientific Revolutions by Thomas Kuhn. Some similarities between the two thinkers are pointed out (e. g. use of incommensurability concept, reference to gestalt psychology, theory-ladenness of observation, view on scientific literature). Yet Fleck’s views differs from Kuhn’s in some important respects (e. g. views on stabilisation, absence of counterpart of scientific revolutions in Fleck’s theory). Contrary to the prevailing view, these differences preclude consideration of Fleck as a forerunner of Kuhn. For this reason, the present paper mentions also possibility of presentation of Fleck’s views in another context which is deemed more helpful: French epistemology (e. g. Canguilhem, Hacking).