Results None of these N-nitroso-N-(p-substituted-benzyl)-methylamines was mutagenic without activation. With activation by the hamster S9 mix, a wide range of mutagenicities was observed. The data from a representative mutagenicity dose-response assay are given in Table 11. Based on the slopes of the dose-response curves (Figure l), the order of mutagenic potency of the test compounds was as follows: p-chloro> p-cyano> p-nitro> p- ...