In this retrospective study 141 HIV positive subjects were included. Allergy was studied by a specific questionnaire and the Phadia Top Test, an in vitro screening test for specific IgE. Both were related to the patients' history, clinical symptoms and the treatment used. Allergy was studied in reference to HIV negative controls and in relation to the clinical and biological subgroups of HIV patients. The statistical analysis (x 2 test) demonstrated a relationship between allergy and HIV infection and the clinical stage of AIDS-IKEL among patients with CD4 > 300 microliters, which may suggest that allergy contributes to the functional deficiency of these cells. We also demonstrated a high frequency of hypersensitivity reactions (75%) in HIV asymptomatic patients with CD4 < 300 microliters, which indicates that allergy could contribute to the early destruction of these cells. The allergic patients declared to be hypersensitive before contamination. Both mechanisms, functional deficiency and destruction of CD4 T-lymphocytes could be the result of the mediators, cytokines and enzymes released from the mast cells during IgE allergic reaction. Thus this study demonstrated that allergy could be a predisposing factor for the contamination and a polyvalent co-factor for the clinical and biologic evolution of HIV infection.