This was an uncontrolled, open-label follow up study of a previous 12-month, randomized, double-blind, placebo-controlled trial performed to assess the long-term efficacy and safety of Recombinant Human Interferon Gamma (rIFN-gamma) in patients with chronic granulomatous disease (CGD). In two centres, 28 patients (24 male, 4 female) with a mean age of 16 years (range 3-37) entered the open-label phase. The patients were treated for a mean of 880 days (range 97-1375 days). Visits were scheduled every 180 days and patients completed one to six visits. rIFN-gamma was administered subcutaneously three times weekly at a dose of 0.05 mg per m2. During the open-label phase of the study 12 patients experienced a serious infection requiring hospitalization within 880 days. The median infection-free time was 993 days. No obvious increase of infections over time was seen. Phagocyte superoxide anion production and phagocyte staphylococcal killing were not influenced by therapy. Seven patients were withdrawn from the study, one because of an adverse reaction, three on their own wish and the other three because they changed to another trial. No patient died during the study. Conclusion. Treatment of patients with CGD with intracellular active antibiotics and additional interferon gamma as infection prophylaxis is safe and justified.