The method here described allows a quantitative study by photonic microscopy of thick material without injuring its structure. A tridimensional photographic model is built through superposing in parallel planes a set of microphotographic transparencies of successive optical cross-optical through the material. This stereomodel exactly features the spatial structure of the object and allows, either directly or by means of a stereogram, to measure its tridimensional coordinates. These data are computerized to obtain linear and angular measurements, and also to produce sets of automacic successive perspective drawings of the object, obtained by rotating the reference axes. The microscope must be fitted up with objectives with a wide numerical aperture and a plane field. An interferential device controls the focusing. The method has been initially worked out to study metaphasic chromosomes in situ within the cell without using any of the customary techniques : squash, hypotonic shock, cross-sections, etc..., which result in a definite loss of information. Basically it is applicable to most of the biological materials, and has produced, as it seems for the fist time in 1968, a tridimensional quantitative study of cellular components by photonic microscopy.