Bovine γ-crystallins were isolated and analysed by electrospray mass spectrometry (ESMS). The mass of γll-crystallin was as predicted from the amino acid sequence and the mass of γlIIb-crystallin was close, but the mass of γlVa-crystallin was 59 Da greater than that expected. γlVa-Crystallin was digested with cyanogen bromide and the fragments were isolated before analysis by ESMS. The masses of the fragments did not correspond to the published sequence. The published sequence of γlVa-crystallin, which has been used to predict its three-dimensional structure, is incorrect.