A soluble form of the complement receptor CD21 (sCD21) is shed from the lymphocyte surface. The amount of sCD21 in serum may modulate immunity as sCD21 levels are correlated with several clinical conditions. We report here the serum levels of sCD21 in juvenile arthritis (JA), systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). Using enzyme-linked immunosorbent assay, we determined sCD21 levels in SLE, SS and JA patients. Mann-Whitney test for nonparametric two-tail P value was performed to obtain statistical significance. Cytometrical analysis of synovial fluid leucocytes of JA patients was done on a FACSsort. While sCD21 levels in SLE and SS are reduced to levels previously found in rheumatoid arthritis (RA), JA sCD21 levels were normal. sCD21 levels did not correlate with clinical parameters and immunophenotype of synovial cells. CD4 T cells in the synovium were almost all of the CD45RO memory type and 13 of 40 patients displayed synovial expansion of γδT cells. CD21 shedding in JA differs from RA/SS/SLE. JA sCD21 levels in synovial fluid are always lower compared to blood levels of the same patients. Analysis of JA synovial T cells indicates a T-cell driven response.