[en] Full-text:Cytokinesis Block Micronucleus (CBMN) Assay is a simple and an alternative way for indicator of chromosome damage. In a large radiation accident, CBMN Assay can be early detect for chromosome damage before we do aberration chromosome assay. After completing 72 hours incubation, cell was harvest and dropped into the slide and will do pre- treatment with RNase A. RNase as an agent to remove residual stainable cytoplasmic material, which will be background of the cell clear. Clear background help to easier in analysis of micronuclei (MN). The diameter of MN usually between 1/16th and 1/3rd of the mean diameter of the main nuclei. The clear image of background useful for slides assessed with automatic image analysis system. (author)