Sensitive assays are required for seroprevalence studies of measles, mumps and rubella (MMR)-vaccinated populations where many may have low levels of antibodies. This protocol describes a quantitative immuno-PCR assay to detect mumps-specific IgG antibodies. The purpose of the protocol is to determine the immune status of individuals to mumps. Mumps-specific IgG from a dilution of patients serum is bound by recombinant mumps nucleoprotein coated on the surface of microtitre plate wells. Bound antibody is detected by PCR using a conjugate of anti-human IgG covalently coupled to an oligonucleotide. The oligonucleotide is detected by the addition of target DNA, designed to hybridise to the oligonucleotide and serve as a template for real-time PCR using the LightCycler. The quantity of target DNA detected by the PCR depends upon the level of specific antibody in the test sample. Crown Copyright (C) 2002 Published by Elsevier Science B.V. All rights reserved.