Food additives are widely used in the food industry and therefore in consumers’ daily diet and are also considered responsible for several adverse health effects. Tartrazine is a well known food colorant that is extensively used in food industry. The observed toxicological effects of tartrazine in addition with the inconclusive results on cytotoxic effects triggered us to study the toxicity of tartrazine in terms of DNA-content alterations using the well known experimental model of protozoan Tetrahymena pyriformis and DNA image analysis. For this purpose, 0.02 and 0.1 M of tartrazine were administered for 3, 6 and 24 hours to protozoan cultures and the macronuclear DNA content of Feulgen stained T. pyriformis nuclei was performed. The preliminary results showed that tartrazine, under the experimental conditions tested, induces a dose dependent increase in the DNA content of T. pyriformis macronuclei. This increase suggests a stimulation of the mitotic process and a genomic alteration, caused by tartrazine.