Abstract: The use of the change in relative frequency of aptamers in a library selected against at least one sample from at least one reference subject of known outcome, prior to and following selection of said library against a sample from a subject, as a means of diagnosing a medical state, disease or condition in said subject. Also, methods for diagnosing a medical state, disease or condition in a subject, involving correlating changes in relative frequency between aptamers to a medical state, disease or condition and diagnosing the subject based on the determined correlations.