Abstract: In a slide coloring apparatus for smear preparations, the slides are placed into small cavities, at a distance from the cavity bottom such that the reagents provided for the coloring are spread on each slide by capillarity.The cavities are provided in the peripheral zone of a circular tray which is capable of rotating at a more or less high speed. The cavities are open toward the edge of the tray, and are separated by swellings. Each reagent is poured into the central zone of the tray and it flows into the cavities by centrifugal action, with the tray rotating at a low speed. After the time needed for each reaction, the reagent is evacuated through the edge of the tray, by centrifugal action, with the tray then rotating at high speed.The invention is especially usable for coloring blood smear preparations.