In the present paper, we have studied the effects of interferon (IFN) -alpha and IFN-beta on the oxidative burst (OB) responses in monocytes and monocyte-derived macrophages from patients with a relatively early phase of HIV infection. We found that in monocytes from patients with HIV infection, the defective OB response could be partially restored by pretreatment with IFN-beta when the cells were challenged with zymosan. No such stimulatory effect was seen in the control groups. In monocyte-derived macrophages, both IFN-alpha and IFN-beta stimulated the phorbol myristate acetate (PMA) induced OB response in the patient group as well as in the blood donor control group. Generation of an OB is an important part of the antimicrobial defence of mononuclear phagocytes. The positive effects of IFN on the OB responses of monocytes and macrophages from patients with HIV infection may be of importance when IFNs are considered in the treatment of HIV-related disease.