The relative limiting concentrations of triplet excited states of tryp
tophar and tyrosine residues have been measured by the ESR method. The
magnitude of limiting concentration of the tryptophan and tyrosine re
sidues T1-states does not vary to fit their numbers in some proteins.
A limitation on the concentration of T1-stales is accounted for by the
fact that in protein molecules there occurs the radiationless excitat
ion energy transfer of chromophores on residues in the triplet state.