As an effective aid to further develop the strategies for extended amino acid sequence determinations, the use of fluorescamine (fluram) as a novel blocking reagent to chemically reduce the newly generated amino termini responsible for the progressively increasing background is described. The method involves interruption of the run when proline has been determined to be the amino terminus, deletion of PITC delivery, in situ treatment of the sample with fluram within the spinning cup extraction of the reaction products using an ethyl acetate: benzene mixture, HFBA delivery, and second extraction with 1-chlorobutane. The normal program is then allowed to continue until the next proline is reached and the entire extended sequence information on nanomole amounts of proteins. The efficiency of the method has been demonstrated by direct comparison of the results of sequence analysis of amyloid P-component with (63 residues) and without (46 residues) fluram treatment. © 1981.