The mutual interference between the second-derivative bands of tyrosine and tryptophan in proteins has been evaluated in terms of the ratio r between two peak to peak distances. The r values have been found to be not only related to the tyrosine/tryptophan ratio but also dependent on the polarity of the medium in which tyrosyl residues are embedded. The results obtained on purified proteins have been found consistent with the available X-ray information and with the existing solvent perturbation data.