Cytological observations on meiotic cells of barley plants (Hordeum vulgare) grown after seed treatment (1000 ppm, 12 hr.), or seedling spraying (500 ppm), with one of 15 pesticides (herbicides Alanap-3, Atrazine, Banvel-D, Cytrol, Embutox E, Hyvar X, Lorox, Monuron, Simazine; insecticides: Endrin, Phosphamidon, Sevin; insect chemosterilants: ENT-50612, Botran) indicated that all of the pesticides were capable of inducing chromosome aberrations and, in certain cases, abnormal cellular behavior, such as cytoplasmic furrowing. The chromosomal aberrations observed included stickiness, extreme clumping or coalescence ("chromatin bodies"), chromosome bridges, fragments, and micronuclei. In addition, asynchronous nuclear and cellular division were observed. Chromosome aberrations in meiotic cells of C1 generation plants ranged from 0.26 to 66.50% and in the C2 generation from 0 to 11.34%. Chromosome aberrations in meiotic cells of plants after spraying the seedlings ranged from 0 to 8.70%. Certain pesticide treatments produced chromosome aberrations in the C1 or the C2 generation which exceeded the X-ray (5,500 R) and ethymethanesulfonate (EMS, 1000 ppm, 12 hr.) treatments used for comparative purposes.