Immunoglobulin patterns were investigated in seventy-three volunteers older than 95 years. An idiopathic paraproteinaemia was found in 19% of the cases. A restriction of heterogeneity and an imbalance in the kappa/lambda ratio of the immunoglobulins was seen in a number of other sera. Determinations of immunoglobulin levels in sera of individuals without paraproteinaemia showed an increase in IgA and IgG. The quantitations of the IgG subclasses demonstrated that an increase in the IgG1 and IgG3 subclasses is responsible for the elevated level of the IgG. The variation in the immunoglobulin levels increased significantly with age of IgM and for the three major IgG subclasses. No abnormalities were found in the urine or in the mixed saliva. These results indicate that selective changes in the extent of the antibody-immunoglobulin repertoire characterize the immunoglobulin pattern of ageing man.