- Concurrent vehicle negative and positive control data : The negative control mutant frequencies were all in the regular range. The strain specific positive control compounds, namely daunomycin, N-ethyl-N'-nitro-N-nitrosoguanidine, 9-aminoacridine, and cumene hydroperoxide in the absence of S9 mix, yielded the expected mutant frequencies that were greatly in excess of the negative controls. The genotype of the tester strains used was thus confirmed. 2-Aminoanthracene and benzo[a]pyrene, which require metabolic activation, were strongly mutagenic. This indicates that the exogenous metabolizing system used in the present investigation (S9 mix) was functioning.