Different plots of Olli barley, Thatcher common wheat, and Stewart durum wheat were each sprayed with a single treatment of 2,4-D. The spraying was done at three-day intervals from emergence to heading time in order to study the effect of the herbicide when applied to plants at various developmental stages. An ester formulation equivalent to 12 oz. acid in 40 gal. of water per acre was used in all cases. Meiosis was studied in spikes obtained from plants of treated and untreated check plots. This material was fixed and stored in Carnoy's Fluid A. Meiotic irregularities were induced by the treatment in some plants of each of the three cereals at all stages of growth. The percentages of abnormal metaphases and anaphases ranged from 0.0 to 35.3 in barley, 0.0 to 33.3 in durum wheat, and 0.0 to 25.0 in common wheat. Chromosomal aberrations were of various types including bridges, fragmentation, asynapsis, aneuploidy, polyploidy, chain and ring formation, and in many cases extreme stickiness of chromosomes. These aberrations are similar to those induced by X irradiation or other mutagens. It is important to determine whether chromosomal aberrations in treated plants are transmissible and also whether gene mutations have been induced. Cytogenetical studies are under way on progenies of treated plants.