The molecular weights of alpha and beta hemoglobin chains from 15 different vertebrate animal sources and 2 common human variants were determined by electrospray mass spectrometry and compared to the calculated masses based on published amino acid sequences. Conjugates were prepared for 14 of the globins using 2 traditional colorimetric derivatizing reagents, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and trinitrobenzenesulfonic acid (TNBS), and the mass of each conjugate was determined by mass spectrometry.