A method of identifying a candidate diagnostic or therapeutic antibody, the method comprising the following steps: (a) classifying a plurality of monoclonal antibodies into two or more antibody groups comprising the following steps: preparing a plurality of antibodies recognizing a cell surface antigen; bringing each of the antibodies into contact with cells of the same kind expressing the cell surface antigen; analyzing each cell after step by flow cytometry so as to obtain data showing reactivity between the antibody and the cell surface, wherein the data are shown in a histogram showing a relationship between a binding amount of antibodies and a number of cells; and comparing the obtained data and classifying antibodies based on the similarity of the data; wherein a plurality of antibodies having the identical or highly similar data are classified into one antibody group, wherein when two data to be compared have similar values in terms of employed parameters, the similarity between the two data is determined to be high and when the difference between two values (100 x (A-B) / A (%) when the two values are A, B (A ≥ B)) is within 10% the two values are determined to be similar; and wherein the parameters are selected from median value, mode, maximum value, range, standard deviation, kurtosis, and skewness of the histogram. (b) selecting two or more groups from the antibody groups classified in step (a); (c) determining the reactivity of a first monoclonal antibody selected from the antibody groups to a clinical sample derived from a patient having a certain disease; and (d) selecting a second monoclonal antibody from the antibody group to which the antibody identified in step (c) belongs as the candidate antibody. (a) classifying a plurality of monoclonal antibodies into two or more antibody groups comprising the following steps: preparing a plurality of antibodies recognizing a cell surface antigen; bringing each of the antibodies into contact with cells of the same kind expressing the cell surface antigen; analyzing each cell after step by flow cytometry so as to obtain data showing reactivity between the antibody and the cell surface, wherein the data are shown in a histogram showing a relationship between a binding amount of antibodies and a number of cells; and comparing the obtained data and classifying antibodies based on the similarity of the data; wherein a plurality of antibodies having the identical or highly similar data are classified into one antibody group, wherein when two data to be compared have similar values in terms of employed parameters, the similarity between the two data is determined to be high and when the difference between two values (100 x (A-B) / A (%) when the two values are A, B (A ≥ B)) is within 10% the two values are determined to be similar; and wherein the parameters are selected from median value, mode, maximum value, range, standard deviation, kurtosis, and skewness of the histogram. preparing a plurality of antibodies recognizing a cell surface antigen; bringing each of the antibodies into contact with cells of the same kind expressing the cell surface antigen; analyzing each cell after step by flow cytometry so as to obtain data showing reactivity between the antibody and the cell surface, wherein the data are shown in a histogram showing a relationship between a binding amount of antibodies and a number of cells; and comparing the obtained data and classifying antibodies based on the similarity of the data; wherein a plurality of antibodies having the identical or highly similar data are classified into one antibody group, wherein when two data to be compared have similar values in terms of employed parameters, the similarity between the two data is determined to be high and when the difference between two values (100 x (A-B) / A (%) when the two values are A, B (A ≥ B)) is within 10% the two values are determined to be similar; and wherein the parameters are selected from median value, mode, maximum value, range, standard deviation, kurtosis, and skewness of the histogram. (b) selecting two or more groups from the antibody groups classified in step (a); (c) determining the reactivity of a first monoclonal antibody selected from the antibody groups to a clinical sample derived from a patient having a certain disease; and (d) selecting a second monoclonal antibody from the antibody group to which the antibody identified in step (c) belongs as the candidate antibody.