The fluorescence characteristics of several commercial samples of human serum albumin were examined before and after treatment to remove bound impurities. The emission spectra of the untreated samples varied in shape, and the relative quantum yields with 280 nm excitation varied widely (standard deviation from the mean was 26.4%). Dialysis and charcoal treatment minimized the spectral differences, but the quantum yields still varied (15.3% standard deviation from the mean). Evidence indicated that fluorescent impurities were present in some samples, while nonfluorescent quenching contaminants were present in others. The fluorescence decay kinetics of all human serum albumin samples examined were multiexponential when excited with a picosecond tunable dye laser operated at 294 nm. The decay kinetics of samples said to be “crystalline” differed even after charcoal treatment. The effect of impurities on optical studies of human serum albumin is discussed.