A novel assay for the identification of agents causing aneuploidy is described. This assay takes advantage of allohexaploid wheat in which monosomic and nullisomic cell lineages can be genetically detected. The wheat strain used is homozygous for a pair of recissive alleles (v1) which in homozygous condition interfere with normal pigmentation of the leaves at low temperature, but it is hemizygous ineffective. This locus is in the short arm of chromosome 3B near the centromere. As a consequence of nondisjunction of this chromosome, twin sectors may be detected in which the monosomic cell lineages appear green, whereas the trisomic sectors display white color on a cream-colored background at low temperature. This genetic system can also be used for the detection of deletions or duplications involving the short arm of chromosome 3B. Results show that X-rays, gamma rays, p-fluorophenyl-alanine, 3-amino-triazole, caffeine, vinblastin sulfate, benzo(a)pyrene, and auramine significantly increased aneuploidy, and diethylstilbestrol, sulfacetamide, safrole, and dichlorvos caused some increase of sectoring.