Trypan blue: identification and teratogenic and oncogenic activities of its coloured constituents.

Three coloured substances frequently present as contaminants in commercial samples of trypan blue have been identified as those monoazo dyes in which 4-amino-3,3'-dimethyl-biphenyl, 4-amino-3,3'-dimethyl-4'-hydroxy-biphenyl or omicroc-tolidine are coupled to H-acid. These dyes have been synthesized and, together with purified samples of trypan blue, tested for teratogenic activity in mice and oncogenic activity in rats. Unpurified trypan blue was both teratogenic and oncogenic; purified trypan blue, was teratogenic but only weakly oncogenic; the monoazo dyes possessed neither activity. It is concluded that the main blue component of trypan blue is the teratogenic principle and that some as yet unidentified component of the purple fraction either is the main oncogenic principle or potentiates the action of the blue component.