Patient K.L. with X-linked hypogammaglobulinaemia showed excessive suppressor T-cell activity both in the lymphocytes from the rheumatoid synovial tissue and in the peripheral blood lymphocyte compartment. This was in marked contrast to the findings in the lymphocytes from synovial tissue of patients with classical rheumatoid arthritis (RA), which were clearly deficient in suppressor T-cell activity. These findings further support the existence of distinctly different pathogenetic mechanisms in the two types of rheumatoid inflammation. It also demonstrates that patients with X-linked hypogammaglobulinaemia may have excessive suppressor T-cell activity not only in their peripheral blood lymphocytes but also in local chronic inflammatory tissue such as the rheumatoid joint inflammation.