The present invention provides a method of determining the presence or amount of newly synthesized antibody in a sample in response to an immunogen by detecting the released antibodies or parts thereof in a sample containing lymphocytes which have been disrupted whereby to release the synthesized antibodies or parts thereof associated with said lymphocytes whereby to determine the presence or amount of newly synthesized antibody in said sample, methods of diagnosis using said method and kits for performing the method. The method may also be modified to allow detection of non-specific infection indicators.