We evaluated clinical efficacy and tolerability of recombinant alpha 2a interferon (IFN), in a group of 16 patients with AIDS and ARC, including 3 children. All patients were followed up monthly for clinical and immunological studies. The frequency of oportunistic infections (OI) in AIDS, and the following symptoms in all patients were studied: fever, night sweats, fatigue, diarrhoea, weight loss. Immunological parameters (CD3+, CD4+, CD8+ lymphocytes, skin tests to recall antigens, NK activity, lymphoproliferative response to PHA) were also evaluated. Adult patients were treated with 3-6 million IU of r-alpha 2a IFN daily im for 3 months and the 3 times weekly up to 12 months. Pediatric cases were treated with lower doses of 0.5-1.5 million IU using the same time schedule. We observed clinical improvement and reduction of severe infections in 10/15 evaluable patients (4/4 ARC and 6/11 AIDS). Immunological parameters were transiently improved in one third of cases. We observed only mild side effects in r-alpha IFN treatment. We suggest therapy with r-alpha 2a IFN at low dosage should be tried in patients with AIDS for its beneficial effects on OI development.