The genotoxic potential of acrylamide monomer (AA), a compound familiar as a raw material of polyacrylamide electrophoresis gel, was extensively investigated in vitro. The results were clear cut: AA did not induce any gene mutations in Salmonella/microsome test systems (TA98, TA100, TA1535, TA1537), Escherichia colilmkrosomt assay (WP2 uvrA−) up to a dose of 50 mg AA/plate, or in HPRT-locus in Chinese hamster V79H3 cells (AA, 1–7 mM, 24 h treatment). On the other hand, AA showed a strong positive response: (a) in a Bacillus subtilis spore-rec assay (DNA damage) at 10–50 mg/disc, (b) to a chromosomal structural change test (AA, 2 – 5 mM, 24 h treatment), (c) to a polyploidy test (AA, 1–5 mM, 24 h treatment) in Chinese hamster V79H3 cells, (d) to a cell transformation assay in mouse BALB/c3T3 cells (AA, 1–2 mM, 72 h treatment). Sister chromatid exchange was also weakly but significantly induced by AA (AA, 1–2.5 mM, 24 h treatment) in Chinese hamster V79H3 cells. Carcinogenic potential of AA was reported in mice and rats several years ago. AA thus seems to be a typical clastogenic rodent carcinogen without any gene mutation potential. Furthermore, this experiment showed for the first time positive response of AA to a microbial test system (B.subtilis spore-rec assay).