Disease is frequent in ageing, and the many conflicting results in studies of the ageing process can be due to the presence of factors such as underlying disease or the use of medication. For immunogerontology, a solution to this problem was initiated in 1984 by a working party of EURAGE, the European Community's Concerted Action Programme on Ageing and Diseases. A protocol defining strict admission criteria to studies of ageing, the SENIEUR protocol, was elaborated. This protocol intends to limit the influence of disease and/or medication and to standardize admission criteria to immunogerontological studies. In subjects fulfilling the SENIEUR criteria, we found less immunological defects with ageing than generally stated. This could mean that many studies performed in not-optimally healthy subjects describe defects that are not a consequence of the ageing process, but could be a result of underlying disease or of the influence of medication. For lymphocyte subsets, certain changes are only found in the comparison of SENIEUR groups of young and aged, while other changes are only found when non-healthy groups are compared. The occurrence of monoclonal gammopathies and autoantibodies was increased in ageing, but was also influenced by health status. Experience of other groups, and the objections against the protocol are discussed.