Rotation stress induced by a grammophone turntable has profound effects on the immune system of mice. In the present study, we tested the effect of the method on the weight of lymphoid organs and cellularity of peripheral blood and lymph in rats. After four days (4 X S X 10 X 78 revolutions) the spleen weight was significantly reduced in rotated rats as compared to controls. Small, but not significant, reductions were also seen in body weight gain, thymus weight, inguinal lymph node weight,

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... acic duct lymphocyte number and peripheral blood leukocyte number. After twenty days (20 X 5 X 10 x 78 rpm) the differences between rotated and control animals were smaller and not significant. We conclude that the stress regimen induced a slight temporary reduction in total body lymphocyte number, but that the rats adapted to the situation with time. Consequently, the method cannot be recommended for longterm experiments in rats.