The aim of the present study was to evaluate the immunological status among medical staff occupationally exposed to ionizing radiation at the cardiac catheterisation units of three different University hospitals (Ain Shams, Al Azhar and National Heart Centre at Embaba) in Cairo, Egypt. The individual annual collective dose information was estimated with thermoluminescence dosimetry (TLD) system. It was 0.02 – 0.3 mSv/y 0.42 – 0.94, mSv/y and 1.16 – 8.44 mSv/y for the three hospitals respectively. Venous blood samples were obtained from 60 hospital workes (20 from each hospital) exposed to x-ray during fluoroscopy procedure as well as from 20 people not exposed to ionizing radiation and not working at hospitals, and from 20 people not exposed to ionizing radiation and working at hospitals. Blood samples were assayed for apoptosis percentage in circulating lymphocytes and lymphocyte’s phenotypes CD4 and CD8 and CD4/CD8 ratio. Results revealed significant increase in the apoptosis percentage in circulating lymphocytes, CD4, CD8 and CD4/CD8 ratio. However, the Embaba group, of which the highest level deviated from the latter finding where CD4 and CD4/CD were significantly decreased in comparison with controls and the other two groups of cardiac catheterisation workers. It is concluded that apoptosis percentage in circulating lymphocytes and cell phenotype analysis for lymphocyte phenotypes including CD4, CD8, CD4/CD8 can offer a more precise indicators for radiation exposure to effective low dose levels of ionizing radiation.