The aim of this study was to investigate the genotoxic effects of flunixin meglumine on mice peripheral lymphocytes by in vitro and in vivo/invitro cytokinesis block micronucleus tests (CBMN). Flunixin meglumine was used at concentrations of 25, 50 and 100 mu g/mL for the in vitro assay and 50, 75 and 100 mg/kg for the in vivo/in vitro assay. Mice were treated intraperitonally twice with a 24 h interval and sacrificed 6 h after the last dose. Cardiac blood was taken and added to the cultures for the in vivo/in vitro test. 21 h after the addition of the test compund for the in vitro test, and after the initiation of incubation for in vivo/in vitro test cytokinesis was blocked with the addition of cytochalasin-B and 20 h later the cultures were harvested. In both test systems, a negative and a positive control mitomycin C (MMC) were also included.