A detailed study of the mass spectra of peptides produced by the new technique of fast-atom bombardment is reported. Molecular weights of unmodified peptides containing up to 21 amino acids have been determined. In favourable cases, the molecular-weight determination may be made on as little as 0.1 nmol of sample. Positive-ion and negative-ion spectra are obtained with equal facility. With sample sizes in the range 2-50nmol, sequence information can be obtained in many cases. The technique represents an important contribution to structural studies on peptides, since (i) blocked peptides may be studied, (ii) no prior formation of chemical derivatives is necessary (except for distinction between lysine and glutamine), (iii) sensitivity is good, (iv) large peptides, and, in some cases, mixtures of peptides, can be studied, and (v) the technique is easy to operate, with ions being produced over a long period (5-30 min).
