The visible absorption spectra of two reactive dyes based on the copper phthalocyanine chromophore have been investigated as a function of concentration, temperature, pH, ionic strength, and solvent. The persistence of isosbestic points indicates that an equilibrium exists, over the concentration range investigated, between two forms of the dye only, namely dimer and monomer. The addition of urea exerts a relatively small disaggregating influence on this equilibrium. On the other hand decrease in dielectric constant substantially changes the equilibrium in favour of the monomeric species.