The quenching of the fluorescence of anthracene and some of its meso-derivatives by “heavy atom quenchers” in various solvents has been shown to be dependent on the solvent, the quencher, and especially on the nature of the substituent. Anthracene shows good agreement with the Stern-Volmer equation in all solvents even in the presence of very high concentrations of quencher. However, marked deviations from this equation are observed for certain anthracene derivatives and in some cases the heavy atom “quencher” leads to an increase rather than to a decrease in the fluorescence.