The aim of the study to analyze the circulating white blood cells including the intensity expression of surface receptors and cytoplasmic molecules in patients underwent total hip replacement, with either aseptic or septic loosening of hip prostheses in order to identify cell-surface and cytoplasmic markers that could be indicative of early loosening. Flow cytometry was performed in whole peripheral blood samples of 20 patients with loosening (10 septic and 10 aseptic). Ten healthy individuals served a control group. The CD62L, CD18, CD11a, CD11b and CD11c expressions were evaluated. The mean fluorescence intensity (MFI) of CD 18 was decreased on all leukocytes subsets compared to control group. For patients with aseptic loosening we demonstrated an increase of MFI for CD11b in granulocytes and for CD11c in monocytes and granulocytes compared to control group. In patients with septic loosening an increase of MFI for CD 11c was observed in monocytes compared to control group. The comparison between aseptic and septic loosening showed a statistically significant lower CD18 MFI value in granulocytes for aseptic loosening. A trend towards lower MFI values of CD 62L in lymphocytes and granulocytes were observed in aseptic but not in septic loosening patients compared to control group. The present study is the first study in published literature to demonstrate cell surface and cytoplasmic markers in peripheral blood indicative of loosening of THAs by means of flow cytometry.