The invention relates to the preparation of thin tissue sections for mass spectrometric (MALDI) imaging, and proposes a method wherein a microcrystalline layer of the matrix material is produced on the surface of the thin tissue sections, and soluble analyte molecules are transported orthogonally through the thin tissue section to the matrix layer, without substantial lateral diffusion, by means of a solvent flow with alternating or constant direction, and are then deposited in the matrix layer and, if possible, embedded in the matrix crystals. A solvent flow which alternates in direction can be produced by successive, alternating phases of swelling and drying, brought about by periodic changes to the thin tissue section temperature and/or the partial pressures of the solvents. A continuous solvent flow can be generated by applying the thin tissue section onto a porous support which supplies solvent to the rear surface of the thin tissue section.