 the analysis of micronuclei ( mn ) in cultured human lymphocytes is , in principle , able to detect exposure to clastogens and aneuploidogens alike . 
 there is , however , no clear evidence from human biomonitoring studies or animal experiments showing that in vivo exposure of resting lymphocytes to an aneuploidogen could actually be expressed as mn in cultured lymphocytes . in vitro , a pulse treatment of human lymphocytes with vinblastine , an aneuploidogen , did result in mn induction even if performed before mitogen stimulation , although a much more pronounced effect was obtained in actively dividing lymphocyte cultures . on the other hand , 
 it is probable that a considerable portion of " spontaneous " mn contain whole chromosomes , their contribution increasing with age . 
 it also seems that cytochalasin b , used for the identification of second cell cycle interphase cells in the mn assay , is able to slightly increase the level of mn with whole chromosomes . 
 if mn harboring chromosome fragments represent a minority of the total mn frequency , there may be difficulties in detecting a weak effect in this fraction of mn against the background of mn with whole chromosomes . 
 this would reduce the sensitivity of the assay in detecting clastogens , unless mn with whole chromosomes and chromosome fragments are distinguished from each other . that a problem may exist in sensitivity 
 is suggested by the difficulty in demonstrating mn induction by smoking , an exposure capable of inducing chromosome aberrations . 
 the sensitivity of the lymphocyte mn assay could be increased by detecting kinetochore or centromere in mn , or by automation , allowing more cells to be analyzed.imagesfigure 2 . 
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