An elevated expression of the alloantigen D8/17 on B lymphocytes has been previously proposed as a susceptibility marker in rheumatic fever. The aim of the study was to investigate the presence of the D8/17 marker on B lymphocytes in poststreptococcal reactive arthritis (PSRA). The study sample included 19 patients (15 boys, 4 girls; mean age 11.7 +/- 5.4 years) who were diagnosed with PSRA (mean age at diagnosis, 9.4 +/- 5.6 years) and 18 healthy controls (10 boys and 8 girls) matched for ethnic background. B-cell D8/17 expression was tested by flow cytometry assay using monoclonal antibodies. Laboratory results showed a higher expression of D8/17 in the patient group (23.1 +/- 10.4%, range 11.6-51.9%) than in the control group (17.1 +/- 8.2%, range 7.1-35.7) in controls; this difference was statistically significant after log transformation of the data (P = 0.035). The high rate of expression of the D8/17 marker in patients with PSRA suggests that RF and PSRA share the same genetic susceptibility.