In structural studies of a human leukemia antigen, the cells of patients with acute lymphoblastic leukemia (ALL) often display a common cell-surface antigen termed CALLA. CALLA is a glycoprotein of 100,000 molecular weight. CALLA-specific monoclonal antibodies have been used to immunoprecipitate CALLAs from a variety of radioiodinated leukemia cell lines and to compare them by two-dimensional (2D) gel electrophoresis. In the study on melanoma surface antigen p97 as related to transferrin, we have identified a human melanoma cell-surface protein as an iron receptor. A small amount of monoclonal antibody directed against the cell-surface glycoprotein p97, which is found predominantly on melanoma cells, was added to a lysate of cultured cells. The antigen-antibody complex, along with a slight excess of the monoclonal antibody, was isolated from the crude lysate passage through a column containing Staphylococcus aureus protein A. After washing, the pH was lowered to elute the monoclonal antibody and the antigen. These proteins were separated and stained. The stained antigen was electrophoretically eluted and the amino terminal sequence was determined in the new microsequenator. A computer search identified the amino acid sequence as being closely related, but not identical, to known members of the transferrin family of iron-binding proteins. The cell-surface molecule was tested and found to bind iron. We have built a new type of microsequenator for peptides and proteins that uses (a) gas-phase reagents at critical points in the Edman degradation and (b) a cartridge-style reaction cell. This new sequenator is particularly suitable for recombinant DNA technology. Also, an advanced type of automated peptide synthesizer is under construction, and a very effective automatic DNA synthesizer has been completed. Both of these instruments will allow for the rapid synthesis of substantial quantities of rare proteins and peptides and for the synthesis of DNA probes and genes. Both of these automated synthesizers make use of amino acid sequence information.