Mutation Research, 263 (1991) 115-117 © 1991 ElsevierSciencePublishers B.V. 0165-7992/91/$03.50 ADONIS 016579929100049F MUTLET 0498 115 Activity of aniline in the mouse bone marrow micronucleus assay J. Ashby 1, D.A. Vlachos2 and H. TinwelP 11C1 Central Toxicological Laboratory, Alderley Park, Macclesfield, Ches. SKIO 4TJ (Great Britain) and 2 Ciba-Geigy Corporation, Agricultural Division, Greensboro, N C 27419 (U.S.A.) (Received28 January 1991) (Accepted 7 February 1991) Keywords: Aniline; Mouse; Bone-marrow MN assay Summary Aniline gave a positive response in the mouse bone marrow micronucleus assay 24 h after the second of two intraperitoneal injections of 80% of the median lethal dose (MLD). Negative results were observed at lower dose levels and at earlier and later sampling times. The significance of this unique activity profile is discussed within the context of the non-carcinogenicity of aniline to the mouse. Aniline is carcinogenic to the rat but not the mouse (Anon., 1978). It is reported also to give a positive test response in a rat bone-marrow micronucleus assay (George et al., 1990). The possible activity of aniline in a mouse bone- marrow micronucleus assay therefore became of particular interest. This interest was enhanced by our recent observation of negative rat and mouse bone-marrow micronucleus assay data for the po- tent rat/mouse carcinogen 2-methoxyaniline (o- anisidine, Ashby et al., 1991). Both chemicals are biologically available as evidenced by their induc- tion of methaemoglobinaemia (cyanosis) in both species of test animal (Anon., 1978; Ashby et al., 1991). Correspondence: Dr. J. Ashby, ICI Central Toxicology Laboratory, Alderley Park, Macclesfield, Ches. SKI0 4TJ (Great Britain). Materials and methods Chemicals. Aniline was re-distilled from AnalaR grade material (BDH). Cyclophosphamide (CP) was obtained from the Sigma Chemical Com- pany, Poole, Dorset. Each was dissolved in sterile deionized water and administered to mice by in- traperitoneal injection (10 ml/kg bodyweight), Micronucleus assays. Bone-marrow smears were prepared and stained with acridine orange as described earlier (Tinwell and Ashby, 1989). 2000 polychromatic erythrocytes (PE) were assessed for micronucleated PE (MPE) on a single slide prepared from each animal. The ratio of PE to nor- mocytes (NE) was determined among 1000 erythrocytes on the same slide. Animals. Male CBA mice aged 8-11 weeks