Abstract: The present invention provides a method for producing proteins with a desired function, generally comprising the steps of (a) providing a population of antibody-forming cells suspected of containing at least one cell capable of producing an antibody exhibiting a desired function; (b) suspending the population of antibody-forming cells in a medium, the medium having an indicator system incorporated therein, the indicator system also being capable of indicating the presence and location of a cell which forms antibodies exhibiting the desired function; (c) identifying a cell forming an antibody exhibiting the desired function; (d) isolating the identified antibody-forming cell from the medium; (e) determining the amino acid sequence of the variable region or a portion thereof which coffers the desired function of the antibody produced by the isolated antibody-forming cell; and (f) synthesizing a protein with a desired function, the protein containing the amino acid sequence of the variable region or portion ther