The effect of two DNA repair inhibitors in bacteria, cobalt chloride and cinnamaldehyde, on 5-azacytidine (5-AC)-induced digital malformations was studied. Both agents inhibited the induced digital malformations. The effect of cobalt chloride was significant 3 hr before to 1 hr after the 5-AC treatment, and the effect of cinnamaldehyde was significant 3 hr before to 24 hr after the treatment. However, an increase in fetal mortality was observed with the latter agent. The mechanisms underlying the suppressive effects of both agents may be different, but their natures require elucidation.