Front face fluorometry allows for the detection of intrinsic fluorescence in intact hemoglobins, and we have been able to assign the origin of this emission in Hb A to the tryptophan at beta 37 (Hirsch, R. E., Zukin, R. S., and Nagel, R. L. (1980) Biochem. Biophys. Res. Commun. 93, 432-439). We now report that this fluorescence in hemoglobin is sensitive to the R leads to T conformational transition. Comparison between liganded states of Hb A suggest a difference in the R structures of HbCO and HbO2. The T state induced by inositol hexaphosphate in the presence of methemoglobin A appears to be different from the T state of deoxyHb A. In agreement with chemical data our fluorescence studies of Hb H indicate that no R to T transition occurs in this hemoglobin, secondary to ligand binding. A slight conformational difference exists between deoxyHbH and COHbH. Hb Beth Israel, a low oxygen affinity mutant, shows unique fluorescence properties suggesting significant differences between the R and T forms relative to those of Hb A.