The cytogenetic effect of the herbicide ''Dicamba'' was investigated in mouse spleen,bone marrow and testes, Swiss mice were intraperitoneally injected with 20 mg kg(-1) body wt ''Dicamba'' (1/10 LD(50)), and killed 6, 24 and 48h. after injection,In another experiment mice were orally treated by gavage. Single and multiple treatments for 3 and 5 days were conducted with the dose 119 mg kg(-1) body wt. (1/10 LD(50)) and mice were sacrificed 24 h. after the last treatment. The percentage of cells with chromosome aberrations was high after excluding the number of metaphases with gaps. The effect of ''Dicamba'' was maximal 6 h. after intraperitoneal injection in both somatic and germ cells. Oral treatment induced also a high percentage of cells with chromosome aberrations in mouse bone marrow, spleen and germ cells. This percentage was statistically significant from the control and increased with increasing the number of treatments with the herbicide The dominant chromosome aberrations were gaps fragments, chromatid deletions in somatic cells and autosomal x-y univalents and polyploid in germ cells. The present results indicate that ''Dicamba'' is genetoxic in : mouse bone marrow,mouse spleen,and mouse testes.