The effect of stress on the recombination frequencies at the 1st and 2nd chromosomes of male mice was shown earlier. The purpose of this work is the study of the stress effects on the behaviour of meiotic chromosomes. Male mice (A/He and DD/J inbred strains) were treated with acute immobilizing stress at different periods, prior to killing. It was shown that the stress significantly increases the frequency of X-Y and autosomal univalents in metaphase 1 and aneuploidy in metaphase 2. The most sensitive to the stress are the late interphase - early leptotene cells.