The aim of this study is to investigate some aspects of immunologic response among Egyptian addicts. The study was conducted on 33 drug addicts who were admitted to hospital for treatment. They were males with age range (19-30; mean 24.73 years). They were followed up at 2-weeks intervals for one month. Blood samples from 18 addicts and 10 non-drug-user control blood donors were evaluated for some lymphocyte immunophenotypic markers by flow cytometric analysis. Addicts showed significantly (P < 0.001) decreased percentages of both T-helper (CD4+ ) and Tcytotoxic (CD8+ ) compared with controls. There was also significant (P < 0.05) reduction of CD4+ /CD8+ lymphocyte ratio. Sera from all addicts, whether on hospital admission or follow-up samples were subjected to the following investigations. Some blood-borne viral infections were investigated; hepatitis B surface antigen (HBsAg) was present in 1/33 (3%) addicts. Hepatitis C virus antibodies (anti-HCV) were detected in 11/33 (33.3%) addicts versus 1/10 (10%) of controls. Human immunodeficiency virus antibodies (anti-HIV) were present in one serum out of 33 (3%) addicts. Reactivation of cytomegalovirus (CMV) latent infection was assessed by detection of anti-CMV IgM in 1/33 (3%) of addicts on hospital admission, which persisted during the first two weeks, then disappeared on the 4th week. Antibody activity as neutralizing antibodies to polioviruses 1,2 and 3 were tested in cell culture, the antibody titer was higher in follow-up samples than on the time of hospital admission. Antistreptolysin O (ASO) was detected in serum of one addict (3%) on hospital admission and in another addict 2- weeks later which indicated streptococcal infection. The acute inflammation phase Creactive protein (CRP) was high in 7/33 (21.2%), 3/33 (9.1%) and 1/33 (3%) upon hospital admission, 2-weeks and 4-weeks, after cessation of drug use respectively.