Malachite green, an N-methylated diaminotriphenylmethane dye, is used primarily as a therapeutic agent in aquaculture. It controls fungal attacks, protozoan infections and some other diseases caused by helminths on a wide variety of fish and other aquatic organisms. In solution, the dye exists as a mixture of the cation (chromatic malachite green) and its carbinol base, with the ratio depending on the pH of the solution; the dye also can undergo chemical and metabolic reduction to a leuco derivative. Malachite green intercalates with DNA, with a preference for A:T-rich regions, and the leuco derivative bears a structural resemblance to carcinogenic aromatic amines that can form covalent DNA adducts. In mammalian cells, it shows marked cytotoxicity and the ability to induce cell transformation and lipid peroxidation. The toxicity of this dye increases with exposure time, temperature and concentration. It has been reported to cause carcinogenesis, mutagenesis, chromosomal fractures, teratogenecity and respiratory toxicity.