Abstract: A microtitration system comprises a plurality of well and a frame-like holder with apertures for receiving the wells. Each well has a bottom wall and a side wall extending upwardly therefrom so as to define an upper open end, and a depression or groove is formed in an outer surface of the well side wall at a position spaced from the bottom wall. Each aperture of the holder is at least partly defined by a resilient aperture defining means, which is adapted to enter into locking engagement with the depression or groove of a well received in the aperture. The dimensions and the shape of each aperture are such that when a well is inserted into the aperture, the aperture defining means is engaging with the outer surface of the well side wall and is pressed radially outwardly in relation to a central axis of the well till the aperture defining means may snap into locking engagement with the depression or groove formed in the side wall of the well.