The determination of the chromosome number in sections or smears of the peanut plant (Arachis hypogaea L.) is rather difficult because of the small number of cells with polar view of metaphase plates and for the tendency of the peanut chromosomes to clump together. Several techniques were tried in order to overcome these difficulties. The best results were obtained with the following method:(a) pre-treatment of the root tips in a saturated solution of paradichlorobenzene at 16-20°C for 4-8 hours or in a 0,002 M solution of oxyquinoline at 16°C for 6-7 hours; (b) hydrolysis in acetic orcein (2% orcein in 70% acetic acid) and hydrochloric acid in the proportion of 9:1; (c) smear and staining in 1% acetic orcein in 45% acetic acid,Paradichlorobenzene and oxyquinoline produce the c-mitotic effect on the chromosomes of Arachis. Consequentely the number of cells at metaphase is greatly increased and the chromosomes appear shortened and scattered throghout the cell. This makes the countings very easy. Comments about the mode of action of paradichlorobenzene on Arachis chromosomes are made and a detailed schedule of the technique is presented.