The phenotypic characteristics of peripheral blood lymphocytes were investigated in 22 patients suffering from active polymyalgia rheumatica/giant cell arteritis (PMR/GCA) prior to steroid treatment. We observed a significant reduction in the absolute number and the relative percentage of CD4-, CD8+ and CD3+, CD16+ and/or CD56+ cells compared to controls. Fifteen patients were investigated prospectively over a 6-month period of prednisone therapy. At the end of the study CD4-CD8+ cells had increased significantly compared to baselines, CD3+ CD16+ and/or CD56+ cells remained significantly lower when compared to controls. We did not observe any abnormalities in the absolute number and percentage of HLA-DR+ T lymphocytes, CD5+ B cells and NK cell phenotypes before or during steroid treatment. Our study confirms that there was significant increase in the absolute number of CD8+ T cells during steroid treatment in the PMR/GCA patients, but indicates the persistence of an immunological alteration despite the control of disease manifestations.