Galangin, a flavonoid derivative, was tested for its anticlastogenic effect against the induction of chromosome aberrations by bleomycin. For an in vitro assay, galangin (0, 2 x 10(-8), 2 x 10(-7), and 2 x 10(-6) M) was added to mouse spleen lymphocyte cultures together with bleomycin (3 microgram/ml) at 24 h after Con A initiation of cultures. In an in vivo/in vitro experiment, galangin (0, 0.1, 1, 10, and 100 mg/kg) was administered to mice orally twice with a 24-h interval. Mice were killed 8 h later. Spleen lymphocytes were isolated and cultures were made. Bleomycin (3 microgram/ml) was added to the mouse spleen lymphocyte cultures at 24 h after Con A initiation. Both in vitro and in vivo/in vitro cultures were harvested at 42 h after initiation. The harvested cells were used for cytogenetic analyses. The results showed that in vitro or in vivo treatment of lymphocytes with galangin suppressed the induction of chromosome aberrations by bleomycin in a galangin dose-dependent manner. The galangin doses used were non-clastogenic to cells. The data from our in vitro and in vivo/in vitro studies confirmed each other and indicate that galangin is an anticlastogenic agent. The in vivo/in vitro protocol may be a useful means to assay the chemoprotective effects of chemicals in humans.