TKT and lymphoma: In the TK+/– mutation test carried out in mouse lymphoma cells according to OECD Test Guideline 490, the number of colonies were increased after incubation with N,N-dimethyl-p-toluidine concentrations of 0.031 μl/ml and above and metabolic activation; the relative total growth (RTG) was 12% to 15% (Seifried et al. 2006).