Inducible promoters are an important tool for synthetic biology. They enable temporal control of gene expression, as well as controlled expression of toxic genes.However, prior to working with an inducible promoter system, it is important to assess whether the inducer compount might positively or negatively affect growth or viability of the cell.This protocol describes the methodology for toxicity assays in the unicellular cyanobacterium Synechocystis sp. PCC 6803 to quantify its growth in the presence of different concentrations of inducer.