Abstract The paper summarizes the results of our previously published studies testifying the hypothesis of the antimutagenic effect of stobadine (STB) in vivo and in vitro. The micronucleus test was used in in vivo experiments with ICR mice. Oral pretreatment with STB significantly decreased the mutagenic effect of cyclophosphamide (CP) in a concentration-dependent way. The protective effect of STB was confirmed in fetuses of CP-treated mice. STB pretreatment exerted also a radioprotective effect in Co 60-irradiated mice. The ineffectiveness of STB posttreatment is indicative of its effect operative in the initiation of mutagenesis and of its radical-scavenging mechanism. The ability of STB to reduce N-methyl-N′-nitro-N-nitrosoguanidine (MNNG)-induced gene mutations and MNNG-induced calcinosis / Raynaud's phenomenon / esophageal dysmotility / sclerodactyly / telangiectasia variant of scleroderma (CREST)-positive and CREST-negative micronuclei in V79 cells was tested in in vitro experiments. We found that this drug reduced the level of both gene mutations and CREST-negative micronuclei mainly if given as pretreatment before exposure of cells to MNNG. We conclude that STB may have inhibited mutagenesis not only by scavenging reactive oxygen species, but also as a result of induction of metabolic enzymes, which reduced the level of DNA lesions.