The concentrations of soluble CD4 (sCD4) and soluble CD8 (sCD8) were determined in 64 patients with polymyositis/dermatomyositis (PM/MD). The patients with PM/DM had significantly higher concentrations of sCD8, though the concentrations of sCD4 did not significantly increase. Patients with high concentrations of sCD8 tended to have too high concentrations of soluble interleukin-2 receptor (sIL-2R). The patients with high levels of myogenic enzymes tended to have high concentrations of sCD8. The results of a serial study indicated that the concentrations of sCD8 decreased simultaneously with the decrease of the myogenic enzymes. These results may suggest that the activation of CD8+ cells are related to muscular involvement.