Disorders in serum immunoglobulins, beta-2 microglobulin and lymphocyte subpopulations in parenterally drug-addict patients (PDAP) are analyzed. The study is divided in three parts. In the first one, a group of 33 HIV-negative PDAP without intercurrent diseases is compared with a control group of healthy non-addict persons. In the second part, the differences between a group of 58 HIV-negative PDAP and a group of 95 HIV-positive PDAP are studied. In the third part, the differences between the group of HIV-negative PDAP without associated procedures and a subgroup of HIV-positive patients including 31 asymptomatic carriers in phase II, are studied. No statistically significant differences were detected between the control group and the HIV-negative PDAP group. The HIV-positive PDAP group showed lymphocytes CD3, CD4 and a CD4/CD3 ratio statistically lower than the HIV-negative group, as well as a significant increase of the immunoglobulin IgG and beta-2 microglobulin. The same results were obtained when the subgroup of HIV-positive patients in phase II was compared with the group of HIV-negative PDAP without intercurrent diseases. According to these results, we conclude that the immunological disorders detected in PDAP patients seem to be more related with the infection by the human immunodeficiency virus and with other associated infections than with the drug-addiction itself.