Expression of interleukin-2 (IL2) receptors was studied on peripheral blood lymphocytes (PBLs) in 25 patients with bullous pemphigoid. Analysis was carried out by flow cytometry. Without immunosuppressive therapy expression of IL2 receptors only on T cells (CD5) was significantly increased as shown by double staining (11.9% +/- 7.8% vs 2.1% +/- 1% in controls). After 2-3 weeks under immunosuppressive treatment with prednisolone and azathioprine, however, BP lymphocytes did not exhibit any IL2 receptors. PBLs of 18 BP patients showed an increase in IL2 production (1027.4 +/- 670.5 U/ml vs 270 +/- 100 U/ml in controls) during the acute stage of the disease after stimulation with phytohaemagglutinin (PHA)/phorbol myristate acetate (PMA). On the contrary, IL2 production of the same cells in five patients was only in the lowest range of control values after PHA stimulation without PMA (12.5 +/- 29.6 U/ml vs 40 +/- 20 U/ml in controls). Under treatment with immunosuppressants the IL2 production normalized after PHA/PMA stimulation and slightly decreased following PHA stimulation. From these results we conclude that a T-cell activation via activation antigens, as IL2 receptors, and the production of the specific ligand, IL2, may play a role in the pathogenesis of bullous pemphigoid, especially in the earliest stages, and serve as a marker of disease activity.