Method for the examination of cells in a culture medium

The invention relates to a method for the examination of cells ( 20, 38 ) in a culture medium, in particular for in-situ microscopy in a bio-reactor, whereby cells in a sample volume, the depth (d) of which is defined by windows ( 14, 16 ) in the direction of the optical axis of the microscope ( 18 ), are microscopically imaged and are automatically recorded and processed by means of an image processing system ( 30 ). Said method is characterized in that the depth (d) of the sample volume ( 12 ) is adjusted to the size of the cells ( 20, 38 ) by successively reducing the separation (d) of the windows while the image size (G) of the cells is simultaneously verified by the image processing system ( 30 ) such that a separation value (D) is determined at which the image size (G) of the cells begins to grow, thus corresponding to flattening caused by the contact pressure of the windows ( 14, 16 ), and that the separation (d) of the windows ( 14, 16 ) is set to said separation value (D) for the examination.